I can recommend the Tokina 12-24 Richie. It's a nice little lens, and at a pretty good price too. There's a newly updated model, but I wouldn't shy away from the older one at all. The updates are only minor.
The model I have (available for both Canon and Nikon) can be had for around $550 brand new these days. I reckon you can't go wrong for that price.
Tokina also do an 11-16, but it's a little more pricey, and that one will distort quite a lot more on the short end.
The 12-24 isn't too bad at all at 12mm in terms of distortion. It's certainly not approaching fisheye levels or anything.
I don't really have a whole lot at 12mm, but this will give you a rough idea.
Mods, if these are too big, let me know and I'll put smaller ones up.
This one is at 12mm, but I got real close to intentionally distort it a bit.
Both of these two are at 16mm.
