JackConnick:While Alcina got some nice shots, I'd say that is only going to work in very clear water.
Jack
I assume that's in ref to the 18-200 and not the 60mm macro

Great ideas on where to start with lenses so far. You can, of course, follow the Pink Link in my Sig to the Sticky as it has a compilation of various lenses taken from all the threads before this on the same question. There are links and suggestions on where to look for images from specific lenses in there, too. Sometimes it's helpful to get an idea of what you can do by seeing rather than reading. We probably need to get more links to images...
The Tokina 10-17 is the new "It Girl" of lenses for UW and those who have it adore it. You'll need two strobes, really.