I was checking out some free wargaming rules the other day and came across 2085 Warlords of the Wastelands.
I haven't played any post apocalypse games before, unless you count Twilight 2000. But this game looks like a lot of fun, and it's not set for a particular world so you can get creative with it. You can use practically any brand or genre of miniatures you want, and getting creative with some converted minis adds to the enjoyment.
Check out these photos:
Characters from Thundarr The Barbarian!
And Mad Max!
It's a great site, so if you get the chance to check it out, you'll be in for a treat!