Free (or cheap) graphics for use in games and apps?

Folks ..

I need a free (or cheap) collection of graphics, icons etc .. that I can use in Android apps. What are some good collections of graphics/images that others are using and can recommend.

I'm working on my first two android apps. One is a game, the other is a flash cards app. Creating the graphics images myself is a non-starter .. It'd be years of effort and a bad result if I tried to do the images myself.
(I'm sure this question has been asked an answered in this forum before .. so if someone could point me to the appropriate thread .. I'd be appreciative!)

Thanks!