There is a professional-level built-like-a-tank Olympus digital slr, the E-1 for which Ikelite promises a housing in December. There is also a new, more compact and more moderately priced model that uses the same mount coming out that month, the E-300 (with the bizzare name "Evolt" for the USA model), for which Ikelite is developing a housing, and for which Oly promises to deliver their own housing in the spring of 2004.
The Oly 5050 certainly is a capable little camera which I've found a wonderful--and wondwerfully reasonably priced and compact--introduction to underwater photography. I've been so impressed by the brilliant viewfiender, build and feel of the E-1 that I'm in the process of buying one. However, I've decided to keep my 5050 and PT 15 housing and buy Ikelite's DS50 flash kit for it ($450 from Adorama) rather than spring for the $1400 housing from Ikelite. With the external flash and a proper adjustment of settings, one can apparently reduce the shutter lag considerably.
The compact form and smaller size of the Evolt plus a super-bright LCD panel may well make that camera an attractive candidate in the future.
I believe that there were also underwater housings available for the Olympus OM series of film SLR's.