Quote: "can anyone recommend a good site for realistic terrain textures"
Try 3DCafe. They have a decent selection of free models and if things haven't changed recently, there are free textures and other useful freebies as well.
If you have access to any version of Photoshop, why not try searching the web for some tutorials on creating your own textures? The basic tools are already in there, I think. I recently found a Photoshop tut on creating lightening bolt textures that's absolutely amazing. I skipped over many others on making sand textures, dirt, etc. just 'cause I had those already.