Larry,
All good advice here, and you seem like you want more capability without taking out a second mortgage. Many Pros selling their work use what some consider "lower end" bodies and as Mo2vation and others mention spend the majority of your bucks on glass. That way, even if you "upgrade" to a different camera body in 1-2-3 years you can keep using the glass.
Here's my short list of recommended dSLR bodies within reason, plus limited lenses if you want to travel light and shoot UW and above:
Nikon
D80, 200 or 300 (D300 is pricey, though!)
Nikon 18-200 VR for surface
Tokina 10-17mm Fisheye for UW (replaces Nikon 10.5mm and 16mm)
Tokina 35mm Macro (newest one) or Nikon 60mm macro
Canon
Canon Rebel XT, XTi or 40D. Maybe even a used 30D for cheap, cheap, cheap!
Canon 28-135mm IS or 28-105mm USM II lens for surface.
Tokina 10-17mm Fisheye, or Sigma or Canon 15mm Fisheye
Canon 60mm USM macro or the new Tokina 35mm macro
Staying in these brands guarantees more lens choices, etc. Putting the small Fisheye lenses even in a 6" dome port will give you sharper corners because a Fisheye starts out as a 180 degree or so lens. Plus underwater the Fisheye view isn't that noticeable.
A flat port for your macro lens choice will mean you only need two ports to shoot a lot of subject matter.
Buying an Ikelite housing and DS (digital substrobe) strobe(s) will give you iTTL (Nikon) or eTTL2 (Canon) flash control plus manual exposure all in one. Keep ports, cords, arms, strobes if you ever upgrade and sell the body and housing body to someone as a "starter" kit.
All food for thought.......
Hope this helps!
dhaas
David Haas Underwater Photography