I like the Canon 20d with the Ikelite housing. The 20d is a DSLR that can grow with you. Why spend now for something you will replace later. I can shoot several days on a single battery charge. If I want to shoot large frame (coral goupings, divers, wrecks) I use my 17x85 lens and port, for medium size macro (closeup fish, eel, some nudi's) I shoot my 50mm Macro and for real closeup my 100mm macro. Like I said it is a flexible system that can grow with you. Of course it takes great shots on the surface as well. Now it would be the 40d instead of the 20d but the principle is the same. Of course there should be good deals out there on used 20d/30d and housings.
As to why Ikelite? I lost my rig in 50 FFW and didn't find it for 8 weeks. No leaks in the housing seals, the strobes battery compartments didn't leak either. 'nuf said.
If you buy a used DSLR be aware that the shutters are good for about 100K activations so always ask how many frames have been shot.
Mike