Where can I find NPC villages?

This may not be exactly what you're looking for but you'll get to see a village at least. Try a new map with the seed gimmeabreak - it generates a map with a village right at the spawn point.

Oh and while you're there, dig below the well to find the abandoned mine!

[via Minecraft reddit]

There was a tweet from Notch on 10th August saying that, eventually, Towns will have their own biome. How common the biome is, however, will remain to be seen in future updates.

341414797482072298 is a seed where you spawn next to a strong hold and a village! Try it!

You can find villages by going to a place where there is no large body of water ( seas& really big lakes etc.) and they usually live on deserts or flatlands. Some signs I realized in villages is that they have a lava lake which is basically a pool of lava above ground. They tend to have sheep and pigs. The best time to locate a village is at night because a village is bright because of the torches.

P.S.

If you find a village, you might want to raid their chests if you are short on supplies