I'm a big fan of Sony digicams (well manufactured, good image quality, good value for oney), but if I had the money, I'd get a digital SLR.
Right now, I have a 4,1 MPixel Sony DSC-P73 with 3x optical zoom - it should be around 200 bucks, and takes great pictures, both outdoors and of closeby objects such as your aquarium inhabitants.
There are enough brands that offer good camera's in your price range - Sony, Canon, Nikon, Olympus, amongst others. Check out www.dpreview.com to get an overview of what's currently available.
*Moved to The Lounge*