I shoot with a 30D in an Ikelite housing and I'm very happy with its quality and functionality - and it was priced in my range.
I use a 5503 6" dome port with my 28/1.8 and a Sigma 15/2.8 fisheye. I tend to stay away from zooms underwater, no real reason other than I like the confinement in creativity - meaning, less options with the lens means I might have to think more... doesn't always work! Although, I'm looking to add the Tokina 10-17 fisheye at some point.
For macro I use Canon's 100/2.8 with Ikelite's flat macro port (with manual focus, which I don't use...) - only because that was the lens I had to start with for topside shooting. It is a little long for underwater, particularly if you want to shoot subjects in the 2-3 inch range. With the 100 I have to get too far back putting more water inbetween me and the subject. Still, it seems to work for me.
A colleague of mine shoots with the 10-22 behind Ikelite's 8" dome (he uses a 20D) and it seems to work fine, however, some people recommend putting a diopter on the wide rectalinear lenses in order to sharpen the corners of the frame.
As for the Ikelite arms, I have no trouble with them. In fact, it is difficult to tighten them so tight that they do not move at all and that's a good thing, in my opinion. Underwater, if I need to make small adjustments I can do so without loosening the arm and risk having it flop.
I stuck with the brand and use a single Ikelite DS-160 at the moment - I couldn't be happier with it. It recycles fast and the light function really is bright enough to be used as a dive light at night.
Lastly, I think you'll be pleased housing either camera in an Ikelite housing - they are not the smallest housing for a particular camera, but they are simple to operate, easy on the pocketbook and seem just as capable (perhaps with the exception of depth) as other more expensive housings. Besides, when was the last time you saw a crappy photo and said, "That must have been taken with an Ikelite housing."? Yeah, me neither.
Okay, this is it, really. A few photos taken with the gear mentioned:
100/2.8 macro with flat port
28/1.8 and 5503 6" dome
15/2.8 fisheye and 5503 6" dome
Hope that helps.
Lee