You can't help but want to make a 2d overhead or isometric game after looking at some of the art available on OpenGameArt- I'll settle for a little procedural terrain generation:
http://www.openprocessing.org/visuals/?visualID=16704 (click run if it asks about running old java)
The OGA site could use more contributors, as well as better organization to promote the best work- and of course it could be popularized by making use of the content there. I think I'll use this and some variations at the next VJ event I do- I've used recorded video from games before, but even better to generate some game-like imagery live.
Another useful feature would be for terrain tilesets to have a standard connectivity definition file- an ascii file that says which tiles connect best to which neighbors in which direction. Current that's hardcoded into the processing sketch.