post apocalyptic rule sets?

[Infojunky]

I like Savage Worlds and there are a couple of fan conversions here http://www.savageheroes.com/conversions.htm

Then there is the Conversion od Darwin's World to Savage World, which you can get through RPGnow.

Not to mention Savage Showdown with is the Miniatures gaming specific rules, actually they are the same rules mostly.

Necromunda and related also do well, I still consider them as a good source.