I just created an online map and embedded it in our wedding Web site. Check out www.weddingmapper.com for a really cool resource.
update: the how-to-create-an-invite-map guide on wedding mapper is great too, but I highly recommend using powerpoint instead of word. And, if your invitation inserts are tiny like ours, save yourself 5 hours of work and just give your guests the link. I want those 5 hours back.