Just dived in

[sphelps]

If you're looking for lens suggestions for aquariums I'd recommend you get yourself two prime lenses as appose to anything with zoom. Prime lenses are cheaper and take better pictures in terms of clarity and while you can't zoom that feature really isn't needed for aquariums.

A 50mm prime is a pretty common lens, no need for a macro version or the most expensive version which will only vary slightly in the aperture range. It's rare to use some thing like a 1.4 f number for aquarium shots and you'll have to get impossibly close to the subject to take advantage of the macro ability.

Next would be the macro (100mm for Canon I believe), this is probably what I would consider the best lens for aquariums. I prefer a larger lens like say 150mm, (Sigma makes a nice 150mm macro) simply because the larger the lens the further the min focus distance. You can also move the lens back but you can't move the lens through glass.