I've reinstalled c3c with the latest beta patch. But when I look at most screenshots in this site it looks like most people have their c3c appearance modded. Where can I find these mod and which are useful?
Most people use either Sn00py's graphics mod, or WarpStorms watercolor mod. Both can be found in the Apolyton directory (see the link menu in the page top).
Look in Apolyton directory > Files > Civilization III > Graphic > Terrain.