Prepare yourself for a long list...
This is a list of all the songs I liked/loved before (and some after) I became a U2 fan. It is sorted! so the first mentioned are the first that I liked :) (well sort of, can't remember everything :P)
I shall not list all the U2 songs and albums, only the important ones...

U2? Never heard of them
Jefferson Airplane - White Rabbit
Bon Jovi - It's My Life
U2 - New Year's Day I used to call this Newyars Day :P
Patti Smith - Because The Night
Bruce Springsteen - Dancing In The Dark
The Mamas & the Papas - California Dreamin'
The Cure - A Forest
Drs. P - Dodenrit
The Beach Boys - I Get Around
Bob Seger - Turn the Page
U2 - With Or Without You And I used to call this If I
Simple Minds - Belfast Child
The Rolling Stones - Paint It Black
Bruce Springsteen - Born In The U.S.A.
Led Zeppelin - Stairway to Heaven
The Eagles - Hotel California I really hate this song now!
Queen - Bohemian Rhapsody
Deep Purple - Child In Time
Pink Floyd - Brain Damage
+Nirvana - Nirvana
The Rolling Stones - Angie
Meat Loaf - Paradise By The Dashboard Light
+Live - The Distance To Here
+Avril Lavigne - Let Go My first cd
Radiohead - Creep
Melissa Etheridge - Like The Way I Do
Nickelback - How You Remind Me

I begin to like U2
+U2 - Elevation Tour Live from Boston
U2 - Bullet The Blue Sky (Live From Boston)
This was and is my favourite song from Boston :)
The White Stripes - Seven Nation Army
+Wishbone Ash - Live Dates
Siouxsie and the Banshees - Overground
Pearl Jam - Black
Sinéad O'Conner - Troy
Eminem - Sing For The Moment
Linkin Park - Somewhere I Belong
Bruce Springsteen - The River
Procol Harum - A Salty Dog
Japan - Nightporter
Cockney Rebel - Sebastian
Therapy? - Diane
Ten Years After - I Can't Keep From Crying, Sometimes
Stevie Ray Vaughan - Little Wing
Peter Gabriel - Biko

I begin to buy ‘new’ U2 albums
R.E.M. - Everybody Hurts
Talking Heads - Psycho Killer
Red Hot Chili Peppers - Around the World
Uriah Heep - Gypsy
Deep Purple - Lazy
Radiohead - Karma Police
Bruce Springsteen - Thunder Road
The Doors - Unknown Soldier
Tom Petty - Breakdown

U2 Fan
Gary Jules - Mad World
Mark & Clark Band - Worn down piano
Metallica - Frantic
Metallica - St. Anger
Enya - May It Be
Green Day - Holiday
The Dubliners - Sick Note
Di-rect- Blind For You

Real U2 fan
+Passengers - Original Soundtracks 1
+The Who - Tommy
Arcade Fire - Wake up
Foo Fighters - The Pretender
Bruce Springsteen - Pay Me My Money Down
+U2 - No Line On The Horizon!!!

I went to my first two U2 concerts!!!

Radiohead - No Surprises (Thanks go to House M.D.)
The Rolling Stones - As Tears Go By (Also thanks to House)


Conlusion:
The more I love U2, the less I listen to other songs...
Well I don't mind! I LOVE U2! :D