For my Sony I've got a 50 or 55mm macro lens, really great for stuff right up against the glass but almost falls behind my Zeis 16-80 for stuff where I'm shooting greater then a foot or so between lens and subject. In hindsight I should've picked up a 100mm macro lens.

Grizz: For Coral, Macro's are cool you can get polyp sized shots! For non-macro photography I would recommend spending some time with the camera and maybe the 18-55 lens and see if there's a zoom level that you spend more time shooting with then the others, then go buy the corresponding lens in that size but as a non-zoom lens ie a non-macro 55mm lens. The fixed focal length will be faster and can handle a larger range of light conditions so will be better for fast moving subjects like fish.

The Canon 100mm f/2.8 macro is the lens to use. There's now even an IS version of it out. As with all macro lenses, you MUST use a good tripod.