I use a Powershot G2 by Canon. Its a great semi-pro camera although I've been itching for a full SLR digital camera. Too expensive though. I think the only gripe I have with this camera duuringn aquarium photography is I can't get close enough with macro. but what can you do with zoom len ses. There is a macro lens atttachment, but I don't think its worth it.
20G heavily planted tank with Eco Complete
Pressurized CO2, Eheim Ecco 2236, 1 55W and 1 36W bulb