This is the best one I've ever seen, and even supports dual monitors.
I actually bought the full version for 19.95, and don't regret it. It turns this 24" widescreen monitor into a very real looking aquairium. I really like it and feel I'm getting so much more use from the monitor when not actually using the PC.
It's got a trial version as well that is very good, but it does have text and ads. Still, it's very nice.
http://www.dreamaquarium.com/
I actually bought the full version for 19.95, and don't regret it. It turns this 24" widescreen monitor into a very real looking aquairium. I really like it and feel I'm getting so much more use from the monitor when not actually using the PC.
It's got a trial version as well that is very good, but it does have text and ads. Still, it's very nice.
http://www.dreamaquarium.com/