While most Oscar categories require you to actually see the movies to make an informed opinion, all you need for best original song is youtube, especially when you can find the scenes. Yes, if Springsteen's "The Wrestler" had been nominated it probably would have and should have won, but that doesn't stop these three songs from being worthy. Catch these fast, cause I don't know how long the powers that be will let these vids stay online.
"Jai Ho," Slumdog Millionaire
WARNING: This plays at the very end of the movie with clips from throughout, so if you haven't seen Slumdog Millionaire yet, you may be spoiled.
"O Saya," Slumdog Millionaire
This is one of the first scenes of the movie, so enjoy spoiler-free.
"Down to Earth," Wall-E
I could only find the song with credits in French, but that shouldn't matter.