Ooh, loads...most written specifically for the film, some just included on the soundtrack. Always makes me very happy to find something new. Will be looking up some of the above I have not heard yet.
I am one of the few that don't mind youtube comments saying "such and such brought me here"...as I see it, if a song is great then you do not need to be the "first" or "only" one recognising its greatness for it to remain great!
Here are some of mine...
Prophecy Remy Zero The Last kiss
New Slang The Shins Garden State
Shape of my heart Sting Leon
The little things Danny Elfman Wanted
England Scotland and Wales Luke Haines Christy Malry's own double entry
Dead Reckoning instrumental Clint Mansell Smokin' aces
Estasi del Amina instrumental David Sardy Zombieland
Under the milky way The Church Donnie Darko
Analyse Thom Yorke The Prestige
Black swan Thom Yorke A scanner darkly
I've seen it all Thom Yorke/Bjork Dancer in the dark
Can't help falling in love with you version Lick the tins Some kind of wonderful (waves to Lottie) 
Hotel California version by Gypsy Kings The Big Lebowski
Life on mars version by Seu Jorge The Life aquatic
Absolutely Entertaining Mariha Barfuss
Across 110th street Bobby Womack Jackie Brown
Little Boxes version by Loch Lomond The box trolls
Will undoubtedly be more 
Same as with TV:
I am indebted to Scrubs for Peter Gabriel's version of The book of love (finale) and for Men at Work's Overkill.
Ugly Betty for Sebastien Tellier Look which led me to La Ritournelle. Also
Home (Edward Sharpe) and Lost (Coldplay).
Six feet under Breathe me Sia (finale)
Sex and the city La belle et le badboy MC Solaar (finale)
C'mon c'mon Von Bondies
Oh and I heard Once around the block by Badly Drawn boy in a play long before it was released so was
when Bewilderbeast came out.
I usually embarrass myself by running up to a waitress/DJ/shop assistant/bartender shouting What's this?* if I don't know the track...at least with films /tv you can look it up or pause the credits umpteen times
Now of course there's Shazam or whatever it is
- Did this last week. Must be the only person not to have heard Balada Boa before.