I've a compact digital Pentax Optio 4.3 mega pixel and a digital SLR 2.3 MP. There's no comparison between the 2, SLR is the way to go if you want awesome pics. You can get a used one on Ebay within your price range. Check out Olympus 2500L SLR on Ebay, I bought one.
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.
i also recommend sony digi cams....i work in an eletronics dept and sell them to people.....so if u have any questions on cams i can help you....all u got to do is ask....also you dont need any higher than 4 megapixels unless u want to print out like 8X10 pictures then only other thing i would do while you were out is pick up a bigger memory card because the ones that come with cameras only hold about 8-16 pics....so if u have any questions ask
thx for the info I am a big fan of sony porducts and cant order off ebay becuase i have no credit card. So Can u guys tell me exact names of newer sony camera's if there are newer/improved sony digi cams better then the ones in the previous posts? If not thats ok I will check some out in the next 2-3 weeks when I get some money. Thx for all the help.