Seating plan software recommendations (does such a beast even exist?)

I'm getting married soon and am busy with the seating plan, and am running into the usual issues of who sits where: X and Y must sit together, but A and B cannot stand each other etc. The numbers I'm dealing with aren't huge (so the manual option will work just fine), but being of the geeky persuasion, I was wondering if there was any software available to do this for me? Failing an exact match, what should I look for (the problem space, books, reference code) to tweak for my purposes?