Every #1 song on iTunes since early 2007 (some dates are inferred). Take 2007 & 2008 with a grain of salt. I put a (?) next to any date I'm not 100% sure on.
Taylor takes the cake with most #1's. I'm too lazy to calculate the number of days for all of thse right now.
2007.... - Feb 13: Fallout Boy - This Ain't A Scene, It's An Arms Race
Feb 13: Fergie ft. Ludacris - Glamorous (removed)
Feb 13 - Feb 17: Dixie Chicks - Not Ready To Make Nice
Feb 17 - Feb 23: Justin Timberlake - What Goes Around... Comes Around
Feb 23 - Mar 15: Mims - This Is Why I'm Hot
Mar 15 - Mar 22: Fergie ft. Ludacris - Glamorous
Mar 22 - Apr 4: Beyonce & Shakira - Beautiful Liar
Apr 4 - Apr 25: Timbaland, Nelly Furtado & Justin Timberlake - Give It To Me
Apr 25 - May 23: Maroon 5 - Makes Me Wonder
May 23 - June 8: Rihanna ft. Jay-Z - Umbrella (removed)
June 8 - June 9: Shop Boyz - Party Like A Rock Star
June 9 - July 3: Rihanna ft. Jay-Z - Umbrella
July 3 - July 22: Plain White T's - Hey There Delilah
July 22 - July 24: Akon - Sorry Blame It On Me
July 24 - July 27: Plain White T's - Hey There Delilah
July 27 - Aug 19: Sean Kingston - Beautiful Girls
Aug 19 - Aug 24: Jonas Brothers - SOS
Aug 24 - Sept 8: Kanye West - Stronger
Sept 8 - Sept 11: Soulja Boy - Crank That
Sept 11 - Sept 16: Kanye West - Stronger
Sept 16 - Sept 27: Soulja Boy - Crank That
Sept 27 - Oct 14: Britney Spears - Gimme More
Oct 14 - Oct 16: Soulja Boy - Crank That
Oct 16 - Oct 20: Colbie Callait - Bubbly
Oct 20 - Nov 10: Chris Brown ft. T-Pain - Kiss Kiss
Nov 10 - Feb 5/ 2008: Flo Rida ft. T-Pain - Low
2008Feb 5 - Feb 10: Yael Naim - New Soul
Feb 10 - Feb 28: Flo Rida ft. T-Pain - Low
Feb 28: Sara Bareilles - Love Song
Feb 28 - Mar 7: Usher ft. Young Jeezy - Love In This Club
Mar 7 - Mar 13: Jeff Buckley - Hallelujah
Mar 13 - Mar 17: Usher ft. Young Jeezy - Love In This Club
Mar 17 - Mar 25: Leona Lewis - Bleeding Love
Mar 25 - Apr 2: Mariah Carey - Touch My Body
Apr 2 - Apr 24: Madonna & Justin Timberlake - 4 Minutes (Leona #1 combined towards end)
Apr 24 - May 6: Leona Lewis - Bleeding Love
May 6 - May 22: Rihanna - Take A Bow
May 22 - May 29: David Cook - Time Of My Life
May 29 - June 17: Coldplay - Viva La Vida
June 17 - June 23: Katy Perry - I Kissed A Girl
June 23 - June 25: Joe Jonas & Demi Lovato - This Is Me
June 25 - June 30 (?): Jonas Brothers - Burnin' Up
June 30 (?) - July 15: Katy Perry - I Kissed A Girl
July 15 - July 19 (?): Jonas Brothers - Pushin' Me Away
July 19 (?) - ????: Katy Perry - I Kissed A Girl
???? - July 31 (?): Jonas Brothers - Tonight
July 31 (?) - Aug 5: Rihanna - Disturbia
Aug 5 - Aug 8: Jonas Brothers - A Little Bit Longer
Aug 8 - Aug 12: Rihanna - Disturbia
Aug 12 - Aug 15 (?): David Archuleta - Crush
Aug 15 (?) - Aug 20: Rihanna - Disturbia
Aug 20 - Sept 2: T.I. - Whatever You Like
Sept 2 - Sept 19: P!nk - So What
Sept 19 - Sept 26 (?): Kanye West - Love Lockdown
Sept 26 (?) - Sept 30: P!nk - So What
Sept 30 - Oct 7: T.I. ft. Rihanna - Live Your Life
Oct 7 - Oct 13 (?): Britney Spears - Womanizer
Oct 13 (?) - Oct 15: T.I. ft. Rihanna - Live Your Life
Oct 15 - Oct 17: Taylor Swift - Fearless
Oct 17 - Oct 23: Britney Spears - Womanizer
Oct 23 - Oct 30: Beyonce - If I Were A Boy
Oct 30 - Nov 4: Taylor Swift - You're Not Sorry
Nov 4 - Nov 6: Taylor Swift - You Belong With Me
Nov 6 - Nov 13: Kanye West - Heartless
Nov 13 - Nov 15: Taylor Swift - White Horse
Nov 15 - Nov 18: Beyonce - If I Were A Boy
Nov 18 - Dec 3: Beyonce - Single Ladies (Put A Ring On It)
Dec 3 - Dec 19: Britney Spears - Circus
Dec 19 - Dec 26: Beyonce - Single Ladies (Put A Ring On It)
Dec 26 - Jan 20/ 2009: Lady Gaga ft. Colby O'Donis - Just Dance
2009Jan 20 - Jan 21: All American Rejects - Gives You Hell
Jan 21 - Feb 3: Kelly Clarkson - My Life Would Suck Without You
Feb 3 - Feb 10: Eminem ft. 50 Cent & Dr Dre - Crack A Bottle
Feb 10 - Mar 27: Flo Rida ft. Ke$ha - Right Round (removed)
Mar 27 - Mar 31: Lady Gaga - Poker Face
Mar 31 - May 19: Black Eyed Peas - Boom Boom Pow
May 19 - May 20: Linkin Park - New Divide
May 20 - May 22: Glee Cast - Don't Stop Believin'
May 22: Kris Allen - No Boundaries
May 22 - June 10: Black Eyed Peas - Boom Boom Pow
June 10 - June 26: Black Eyed Peas - I Gotta Feeling
June 26 - June 30: Michael Jackson - Man In The Mirror
June 30 - Aug 11: Black Eyed Peas - I Gotta Feeling
Aug 11 - Sept 11: Miley Cyrus - Part In The U.S.A.
Sept 11 - Sept 14: Black Eyed Peas - I Gotta Feeling
Sept 14 - Sept 17: Jay-Z ft. Alicia Keys - Empire State Of Mind
Sept 17 - Sept 19: Drake, Kanye West, Lil Wayne & Eminem - Forever
Sept 19 - Oct 6: Miley Cyrus - Party In The U.S.A.
Oct 6 - Oct 18: Britney Spears - 3
Oct 18 - Oct 19: Miley Cyrus - Party In The U.S.A.
Oct 19 - Oct 27: Owl City - Fireflies
Oct 27 - Oct 31: Taylor Swift - Jump Then Fall
Oct 31 - Nov 5: Owl City - Fireflies
Nov 5: Rihanna - Russian Roulette (for an hour, I think)
Nov 5 - Nov 13: Owl City - Fireflies
Nov 13 - Nov 17: Lady Antebellum - Need You Now
Nov 17 - Dec 12: Lady Gaga - Bad Romance
Dec 12 - Jan 7/ 2010: Ke$ha - Tik Tok
2010Jan 7 - Jan 13: Ke$ha ft. 3OH!3- Blah Blah Blah
Jan 13 - Jan 19: Ke$ha - Tik Tok
Jan 19 - Jan 23: Taylor Swift - Today Was A Fairy Tale
Jan 23 - Jan 24: Jay-Z, Rihanna, Edge & Bono - Stranded
Jan 24 - Jan 25: Taylor Swift - Today Was A Fairy Tale
Jan 25 - Jan 28: Justin Timberlake & Matt Morris - Hallelujah
Jan 28 - Feb 1: Ke$ha - Tik Tok
Feb 1: Black Eyed Peas - Imma Be
Feb 1 - Feb 5: Lady Antebelllum - Need You Now
Feb 5 - Feb 13: Black Eyed Peas - Imma Be
Feb 13 - Feb 20: Artist For Haiti - We Are The World 25: For Haiti
Feb 20 - Mar 2: Black Eyed Peas - Imma Be
Mar 2 - Mar 28: Taio Cruz ft. Ludacris - Break Your Heart
Mar 28 - Apr 15: Train - Hey, Soul Sister
Apr 15 - Apr 26: B.o.B ft. Bruno Mars - Nothin' On You
Apr 26 - May 3: Usher ft. will.i.am - OMG
May 3 - May 11: Eminem - Not Afraid
May 11: Usher ft. will.i.am - OMG (couple hours)
May 11 - May 19: Katy Perry ft. Snoop Dogg - California Gurls
May 19 - May 21: Miley Cyrus - Can't Be Tamed
May 21 - May 26: Usher ft. will.i.am - OMG
May 26 - June 23: Katy Perry ft. Snoop Dogg - California Gurls
June 23 - June 26: Eminem ft. Rihanna - Love The Way You Lie
June 26 - July 7: Katy Perry ft. Snoop Dogg - California Gurls
July 7 - Aug 4: Eminem ft. Rihanna - Love The Way You Lie
Aug 4: Taio Cruz - Dynamite
Aug 4 - Aug 11: Taylor Swift - Mine
Aug 11 - Aug 17: Taio Cruz - Dynamite
Aug 17 - Aug 22 (?): Lil Wayne ft. Drake - Right Above It
Aug 22 (?) - Sept 8: Katy Perry - Teenage Dream
Sept 8 - Sept 14: Bruno Mars - Just The Way You Are
Sept 14 - Sept 22: Rihanna - Only Girl (In The World)
Sept 22 - Sept 24: Glee Cast - Empire State Of Mind
Sept 24 - Sept 29: Bruno Mars - Just The Way You Are
Sept 29: Far East Movement - Like A G6
Sept 29 - Sept 30: Glee Cast - Toxic
Sept 30 - Oct 5: Far East Movement - Like A G6
Oct 5 - Oct 9: Taylor Swift - Speak Now
Oct 9 - Oct 12: Far East Movement - Like A G6
Oct 12 - Oct 16: Taylor Swift - Back To December
Oct 16 - Oct 19: Far East Movement - Like A G6
Oct 19 - Oct 22: Taylor Swift - Mean
Oct 22 - Oct 26: Far East Movement - Like A G6
Oct 26: Taylor Swift - Sparks Fly
Oct 26 - Nov 3: Ke$ha - We R Who We R
Nov 3 - Nov 8: Rihanna ft. Drake - What's My Name
Nov 8 - Nov 9: Ke$ha - We R Who We R
Nov 9 - Nov 13: Glee Cast - Teenage Dream
Nov 13 - Nov 17: Ke$ha - We R Who We R
Nov 17 - Nov 21: Glee Cast - Forget You
Nov 21 - Nov 23: Ke$ha - We R Who We R
Nov 23 - Dec 15: Katy Perry - Firework
Dec 15 - Dec 17: Bruno Mars - Grenade
Dec 17 - Dec 21: Lil Wayne ft. Cory Gunz - 6 Foot 7 Foot
Dec 21 - Jan 11/ 2011: Bruno Mars - Grenade
2011Jan 11 - Jan 22: Britney Spears - Hold It Against Me
Jan 22 - Jan 25: Bruno Mars - Grenade
Jan 25 - Feb 1: P!nk - F**kin Perfect
Feb 1 - Feb 7: Dr Dre ft. Eminem & Skylar Grey - I Need A Doctor
Feb 7: Wiz Khalifa - Black And Yellow
Feb 7 - Feb 9: Black Eyed Peas - The Time (Dirty Bit)
Feb 9 - Feb 11: Glee Cast - Firework
Feb 11: Colbie Callait - I Do (few hours)
Feb 11 - Mar 4: Lady Gaga - Born This Way
Mar 4 - Mar 14: Jennifer Lopez ft. Pitbull - On The Floor
Mar 14 - Mar 16: Katy Perry ft. Kanye West - E.T.
Mar 16 - Mar 18: Glee Cast - Loser Like Me
Mar 18 - Mar 23: Black Eyed Peas - Just Can't Get Enough
Mar 23 - Mar 31: Wiz Khalifa - No Sleep
Mar 31 - Apr 3: Black Eyed Peas - Just Can't Get Enough
Apr 3 - Apr 13: Katy Perry ft. Kanye West - E.T. (not sure when this was removed...)
Apr 13 - Apr 16: Rihanna ft. Britney Spears - S&M remix
Apr 16 - Apr 20: Lady Gaga - Judas
Apr 20 - Apr 24: Adele - Rolling In The Deep
Apr 24 - Apr 26: Katy Perry ft. Kanye West - E.T.
Apr 26 - May 10: Adele - Rolling In The Deep
May 10 - May 11: Lady Gaga - The Edge Of Glory
May 11 - May 26: Adele - Rolling In The Deep
May 26 - May 28: Soctty McCreery - I Love You This Big
May 28 - June 15: Adele - Rolling In The Deep
June 15 - June 22: Katy Perry - Last Friday Night (T.G.I.F.)
June 22 - June 27: Maroon 5 ft. Christina Aguilera - Moves Like Jagger
June 27 - June 29: LMFAO ft. Lauren Bennett & GoonRock - Party Rock Anthem
June 29 - June 30: Dia Frampton - Inventing Shadows (removed)
June 30 - July 12: LMFAO ft. Lauren Bennett & GoonRock - Party Rock Anthem
July 12 - July 15: Demi Lovato - Skyscraper
July 15 - Aug 8: LMFAO ft. Lauren Bennett & GoonRock - Party Rock Anthem
Aug 8 - Aug 16: Maroon 5 ft. Christina Aguilera - Moves Like Jagger
Aug 16 - Aug 21: Lil Wayne ft. Drake - She Will
Aug 21 - Aug 29: Maroon 5 ft. Christina Aguilera - Moves Like Jagger
Aug 29: Foster The People - Pumped Up Kicks (1 hour)
Aug 29 - Sept 10: Adele - Someone Like You
Sept 10 - Sept 27: Maroon 5 ft. Christina Aguilera - Moves Like Jagger
Sept 27 - Sept 28: Adele - Someone Like You
Sept 28 - Oct 1: B.o.B ft. Lil Wayne - Strange Clouds
Oct 1 - Oct 14: Adele - Someone Like You
Oct 14 - Oct 15: Snoop Dogg & Wiz Khalifa ft. Bruno Mars - Young Wild & Free
Oct 15 - Oct 17: LMFAO - Sexy And I Know It
Oct 17 - Oct 19: Justin Bieber - Mistletoe
Oct 19 - Oct 20: Drake ft. Nicki Minaj - Make Me Proud
Oct 20 - Nov 10: Rihanna ft. Calvin Harris - We Found Love
Nov 10 - Nov 11: Taylor Swift - If This Was A Movie
Nov 11 - Nov 16: Rihanna ft. Calvin Harris - We Found Love
Nov 16: Drake ft. Rihanna - Take Care
Nov 16 - Nov 18: Glee Cast - Rumor Has It / Someone Like You
Nov 18 - Nov 22: Rihanna ft. Calvin Harris - We Found Love
Nov 22 - Nov 29: LMFAO - Sexy And I Know It
Nov 29 - Dec 4: Bruno Mars - It Will Rain
Dec 4 - Dec 7: LMFAO - Sexy And I Know It
Dec 7 - Dec 10: Glee Cast - We Are Young
Dec 10 - Dec 23: We Found Love + Sexy And I Know It flip flop like 10 times
Dec 23 - Dec 24: Taylor Swift & The Civil Wars - Safe & Sound
Dec 24 - Jan 4/ 2012: LMFAO - Sexy And I Know It
2012Jan 4 - Jan 12: Jason Mraz - I Won't Give Up
Jan 12 - Jan 18: Adele - Set Fire To The Rain
Jan 18 - Jan 19: Glee Cast - Without You
Jan 19 - Jan 25: David Guetta ft. Nicki Minaj - Turn Me On
Jan 25 - Feb 8: Kelly Clarkson - Stronger (What Doesn't Kill You)
Feb 8 - Feb 12: fun. ft. Janelle Monae - We Are Young
Feb 12 - Feb 14: Whitney Houston - I Will Always Love You
Feb 14 - Feb 22: Katy Perry - Part Of Me
Feb 22 - Mar 26: fun. ft. Janelle Monae - We Are Young
Mar 26 - present: Justin Bieber - Boyfriend