found this on a Ellen forum seems to be mostly pop acts/songs
1. Songs that Ellen Dances to after her monologue
Just Dance - Lady GaGa
Sexyback - Justin Timberlake Ft. Timbaland
Dont Stop the Music - Rihanna
4 Minutes - Madonna Ft. Justin Timberlake
Feedback - Janet Jackson
Tambourine - Eve
I Like That - Houston
Swing Ya Rag - T.I.
Stronger - Kanye West
Do I Do - Stevie Wonder
Closer - Ne-Yo
2. Songs thst artists/bands perform on the show
I Do Not Hook Up - Kelly Clarkson
Since You Been Gone - Kelly Clarkson
Anything, Anything - Dramarama
How Do You Sleep - Jesse McCartney Ft Ludacris
It's Like That - Mariah Carey
Everybody Knows - John Legend
Fallin For You - Colbie Caillat
Just Dance - Lady GaGa
So What - Pink
Funhouse - Pink
Sexyback - Justin Timberlake Ft. Timbaland
Feedback - Janet Jackson
Single Ladies - Beyonce
Blame It - Jamie Foxx
The Fear - Lily Allen
Just A Girl - No Doubt
Hella Good - No Doubt
Right Round - Flo Rida
Stronger -Kanye West
Today - Joshua Radin
3. Songs that guests walk out to
American Boy - Estelle Ft. Kanye West
Glamorous - Fergie Ft. Ludacris
Touch My Body - Mariah Carey
Fantasy - Mariah Carey
Forever - Chris Brown
Just Dance - Lady GaGa
U Cant Touch This - MC Hammer
Straight Up - Paula Abdul
I Kissed A Girl - Katy Perry
Live Your Life - T.I.
5. Other songs related to Ellen/her shows (please say how it relates)
Since You Been Gone - Kelly Clarkson (From the infamous attempts of the audience members trying to sing the right lyrics - Kelly also performed it on the show)
Barracuda - Heart (Ellen plays this on Guitar Hero during a monologue)
Anything, Anything - Dramarama (One of Ellens favourite songs - apparently she always wanted to play it during the commercial breaks, then one day Stryker surprised Ellen by getting them to perform it on the show)
Womanizer - Britney Spears (Ellen sings it when Britney and her go Christmas Carolling, it also plays in the background)
Lets Get It Started - Black Eyed Peas (First song played with the montage of the best moments from the first 1000 shows)
When I Grow Up (Played in the background when Ellen is driving the fire engine whilst meeting her Warner Brothers neighbours)
And I Am Telling You I'm Not Going - Jennifer Hudson (Ellen and Jennifer performed this for the Bathroom Concert Series - HILARIOUS!)
Milkshake - Kelis (Pretty sure its played before "I Scream, You Scream, I Cant See My Ice Cream!")
So What - Pink (Ellen and Pink performed this for the Bathroom Concert Series)
Sexyback - Justin Timberlake Ft. Timbaland (Ellen playes it on the boombox whilst at the Shriners Golf Tournament with Justin, and also makes dance moves up to the song in a Vlog)
D**n Girl - Justin Timberlake (Played in the background when Ellen shows video footage of her photoshoot at W Magazine)
Shut Up And Drive - Rihanna (Played pretty much every time Ellen gives away a car)
Halle Berry (Shes Fine) - Hurricane Chris (Ellen and Halle Berry dance to this on the show when Ellen shows the YouTube videos being made to it)
Gold Digger - Kanye West (Played when people are playing "Gold Digger" and now "Ellens Cash Clunker")
Hot In Herre - Nelly (Played when Portia walks onto her practice interview with Ellen)
I Kissed A Girl - Katy Perry (Ellen and Katy performed this for Ellens Bathroom Concert Series)
Right Round - Flo Rida (Played many times on Ellen, such as when Ellen and Portia play Aw Snap during the practice interview, one of the songs played during the montage of the best moments from the first 1000 shows etc)
Calle Ocho - Pitbull (The song Ellen daced to for the famous Season 7 Premiere dance)
Gimme More - Britney Spears (Played when Paris changes the song in the car when her and Ellen go clubbing)
Stronger - Kanye West (Not sure if this is connected to the talk show, but i found a video on Youtube where Ellen gives a tour of her house, and this song plays in the background when Ellen introduces her "Posse" in the bathroom)
Ribbon in the Sky (Apparently this was Ellen and Portias first slow dance song at their wedding, and i think it was on Ellens playlist on the iPod she signed and auctioned for charity)
Signed, Sealed Delivered, Im Yours - Stevie Wonder (Played when Ellen reads letters in the segment "Signed, Sealed, Delivered")
Work It - Missy Elliott (Played before the game "Whistle While You Work It")
Today - Joshua Radin (I'll call it "Ellen and Portias Wedding Theme Song")
Closer - Ne-Yo (Played during one of the rehearsals, when Ellen sings into the tiny microphone)