1) Take an antique frame (perhaps from a garage sale or your own attic) with lots of curlicues and embellishments - and remove the backing, leaving only the frame.
2) Spray-paint it gold (or silver, or whatever color you wish).
3) Then, take a picture of each guest/group of guests in the frame, having them write their entry in the guest book and later glue the picture to the page.
I have found that giving people any sort of prop makes them less stiff when it comes to photo taking – something about the object breaking the tension, and serving as a nice distraction. The gold (or silver!) frame provides a nice distraction while looking elegant the whole time.
As a nice extra touch, send copies of the pictures to each guest with their thank you note – we have both of ours hanging in our living room, we love them!
In these photos, we just used the background of the reception room. It would be possible, of course, to hang a sheet or some other solid backdrop, to make the frame "pop". This would also be a possible activity with a polaroid camera. In general, it was a lot of fun to do and it allowed the guests to get to know each other too as they were waiting for their photo. Some even formed new groups to get their photo taken later! A cheap alternative to the photobooth idea...