A fun idea for your reception and cocktail hour... have a photobooth.
They are alot of fun and allow your guests to have a picture to take home with them, AND a picture strip to put in your guest book along with their well wishes.
Like the idea of a photobooth, but need something a little less expensive? How about a Polaroid station? Set a Polaroid camera out with your guest book and ask guests to include a picture of themselves in your guest book. Here is an example of one from a wedding I did last year.