Reasonable high end camera;
Canon D10 - $1500
Canon 100 f2.8 macro - $500
Canon 50 f2.5 macro - $300
CF card 512mb - $150
This is a more usable camera for the average shooter, it has built in flash which works better then any built in system I have ever used.
The 1st macro is slightly telephoto and will make shooting easier and stress your fish less. The 2nd will allow you to be closer to subject, while offering a larger field of coverage.
Point and Shoot system
Canon G2 - $500
many professional shooters use this as camera of choice while away from the job. It has many pro features that may benefit your shooting. There is a G3 model, the cost difference is slight, I still prefer the G2.
http://www.powershot.com/powershot2/home.html
If you are looking for digital for in pocket.
Check out the Olympus C-50, metal body and tiny - but pack awesome punch. This I carry every where and love the little guy. Try at office max or staples, then buy online to save $150.00
happy shooting
Pierre