azdesertdiver, you don't mention what kind of photography you want to do. By all accounts, the 10-22 is a great lens, but it is wide-angle only - its range on a DRebel is 35mm equiv 16-35mm. You may not want to purchase an $800 wide-angle lens unless you're sure it's what you want.
I've been diving my dRebel primarily with the kit lens (18-55mm) - it's not an incredible quality lens, but for the little extra it costs, it's worth it. It goes to 1:3 macro ratio, so while not a macro lens it can do pretty good closeups. I've gotten some great UW pictures with it. I'm planning to upgrade to the 17-85mm, as it is a better quality lens, and will be a much better walkaround lens topside. If you're new to UW photography, I would recommend going with one of these two lenses, and not just the 10-22, which will force you to do wide-angle only. Either of these lenses will let you do fairly wide-angle to fairly close-up work, which will let you figure out what you really want to do. My only complaint with the 18-55mm underwater is sharpness, and I'm very picky about that.
My other housed lens is the 100mm f2.8 macro - which is an AWESOME lens. Highly recommended for sharpness - however, it takes some getting used to shooting a 35mm equiv 160mm macro lens underwater. You will not get many full-fish pix with this lens, but it takes incredible macros.
The 50mm f.18 is also one of my favorite lenses for topside. Underwater, I don't know this has a whole lot to specifically recommend it, but it is a great indoor available-light lens. Very very sharp, very small and light, and very fast. I would recommend anyone who has a Canon camera, doesn't own the 50mm f/1.4, and ever takes pictures of people to purchase this lens.
I started out with the 75-300mm non-IS, non-USM. The glass is mostly the same for all three of these lenses, and I gotta say, this is not a great lens. Mine has bad chromatic aberration, not very contrasty, and pretty soft on sharpness. I would save your money and go for the 100-300 or another lens.