I think this is what you are looking forhttp://wiki.answers.com/Q/List_of_PC_games_without_graphic_card_requirementEDIT:
Also try using this software:3d Analyzer
Don't listen to anybody who tells you that it doesn't work!!
I've personally used it and successfully played a few games at a playable fps (25+) on my GMA945 onboard graphics before I got a discrete graphic card.
Although you should remember that this software is NOT a replacement for a discrete graphics.
Games that I've successfully played using 3d Analyzer:
Splinter Cell Chaos theory
Prince of Persia SOT
Far Cry 1
Left for Dead 1&2