Thanks for the replies -- the issue is when the menu wraps onto a second line. The second (and subsequent) lines always seem to align to the left of their container, even if that container is centered.
Here's the page I'm having the issue with:
http://www.control-access8.com/~soulconnection/
If you scroll down to the bottom, you'll see that the links in the footer are centered as a whole, but the individual lines aren't centered relative to each other, and I can't get them to, no matter how many elements I make text-align:center.