[djmcmath]

If you've narrowed it down to Canon and Nikon, you're doing better than 90% of the shopping crowd already. I can't disagree with Todd's opening statement about the quality of Nikon's closeup gear, despite my history as a Canon user.

I would make two recommendations:
1 - If you're serious about making good pictures, spend money on the glass, not the body. It's an old line that we used in the film days, and it's still (mostly) true in the digital era. Whatever you do, don't spend $1200 on a body and $50 on the cheap-o Sigma thing. And please, for the love of god, don't buy a zoom lens for your macro work.
2 - Check photodo.net for lens ratings. They do lens testing, and have done most of the available lenses. Look at the comparable lenses from both Canon and Nikkor, then cross-reference against B&H Photo and Video prices for them.

Dan