Originally Posted by rowan

The Sigma 12-24mm lens is the widest angle full frame lens you can get for a Canon (D)SLR, but its build quality is variable and you could end up with a dud.

I would think twice about buying EF-S lenses (rather than EF) because they will only work on the Digital Rebel and 20D bodies. EF-S lenses are made for the smaller "1.6 times crop" sensors used on those bodies. Think of the future: your lenses will probably last longer than your body, so you're limiting yourself by investing in EF-S lenses. If you ever buy a full frame body (including a film body) then your EF-S lenses will be useless.