I was on the same boat as you a few months ago. From my research, most people like the Tokina fisheye for wide angle, and Canon 50 or 100mm macro for macro. But if they choose either one of the above, they’re stuck with the lens through out the whole dive.
For those who want to do both in one dive, the Sigma 17-70mm is the popular way to go, here is an article about it:
http://underwatervisions.wordpress.com/2010/09/14/the-sigma-17-70mm-%E2%80%93-a-lens-for-the-indecisive/
That lens is not very expensive, f2.8 so it’s quite fast, could do reasonable macro and wide angle. I didn’t get into it because of the whole dome port, zoom gear, not to mention the hosing for my Canon 7D would cost me $2000. Not ready for that kind of investment yet.