For ruined cities check MRX3010's Shattered World series in the marketplace here and Stonemason has some great ruin models over at daz.
Look for "theschell" on share cg or in freebies here for a nice ruined Norman village, his WWII series and I think MrSparky has some ruined/bombed buildings out there somewhere, VP perhaps

If anyone knows of more ruins I'd be glad to hear about them too