I'm a big wide/ultrawide guy, and I'm a huge fan of the Vivitar Ultra Wide and Slim (which was also reincarnated as the Superheadz Wide and Slim). It's a tiny, cheap plastic camera with a 22mm f11 plastic lens.
Fabulous vignette. Spills light brilliantly in areas of high contrast. I'm impossibly in love with it. You'll want something else for shallow DoF effects, but this camera ought to be in your bag as well.