Hi Joe Reefer,
I don't know if you're set on Canon. But may I offer a suggestion. I know the Canon S3 IS is not exactly a compact camera so you may want to move towards a full on DSLR. It's a much better investment. If you don't have lot of experience shooting in manual mode..SLR these days can still provide an auto shot setting. For the price I would go with a cheap slr body such as a Nikon d40 and the Phoenix 100mm 1:1 Macro lense. If your into Canon, I'm sure they have a cheap dslr body as well..and the Phoenix also come in Canon mount. The Ultra Zoom feature won't provide the same sort of benift a true 1:1 macro will give you. At 100mm..you can hit a lot of depth.
Here are some specs
Nikon D40:
http://www.memoryexpress.com/index.p...ctID=9798&SID=
with this budget macro lense that is at 100mm length..perfect for reef tanks...and it's tack sharp and is really inexpensive for a SLR lense:
http://www.photographyreview.com/cat...4_3111crx.aspx
Edit: My bad..this set up will cost 800-900 dollar..might be significantly more than what you are willing to spend. This is a great budget setup for macro photography though.