Wasteland 2 is an obvious one because it's by Brian Fargo, the same Brian Fargo from Fallout. It has the same post nuclear war theme, and the same turn based combat, and is about as close to a Fallout clone as you'll get. Brian Fargo also did the original Wasteland.
I think it's due out this year (don't quote me on that) but the Early Access is available now at Steam if you're into that. Not my cup of tea, but just to let you know.
EDIT: I should add though, probably the biggest difference between Fallout and Wasteland is that Fallout is centered around one character (the vault dweller) while both Wasteland 1 and Wasteland 2 are absolutely party based RPG's. But the setting, mechanics, and I think (but might not be remembering this right) rules are about the same.
Fenixp: Absolutely. If you're interested in a bit more in-depth look,
I made a topic for that.
Other than that, it reminds me of Fallout a lot - while it's got a much more stronger focus on survival and turn-based battles just sort of work differently, there's a lot of focus on freeroaming and exploring a big map, finding quests and making very meaningful decisions, which might come back to bite you in the ass later on. Strongly recommended. It's also a fair bit more polished than Arcanum, altho Arcanum is definitely more Fallout-like.
Oooh, thanks for that link, I had missed that thread. I've got the game from here at gog and hadn't tried it yet. That's going to be pushed up on my list now. Thank you very much. Wish I had seen that thread earlier.