Have a little video camera at the entrance. That way you're guests can sign in and also leave you and your groom a special message and you can save that forever and it will help you when you feel down!
We had a friend take polaroids as the guest as they came in and add them to a photo album on-the-spot. The guests posed -- in couples, groups, whatever. The guests then wrote a little message. It was such a hit! And the breakfast the next morning, everyone wanted to look at the guest book (which I've NEVER heard anyone ever asked to do!). We got the album we used from Adesso -- see http://www.adessoalbums.com/ (they have packages with polaroid cameras and film, too). We also did this at the bridal shower (it was a great trial run). It's a really nice rememberance of the friends who shared these special times with us.
At a wedding I went to the Bride and Groom had their videographer go around all the guests to record personal messages and to recall funny tales about them. It was very embarrassing as I don't think anyone was prepared for what to say but if everyone's notified beforehand they can plan ahead what to say.
They make a photo frame with an especially wide mat for guests to sign. Then you can have your wedding photo and lots of little messages of love on your wall for years.
At our wedding we had a signing plate - each guests signs and writes a message in pencil on an unfinished, unfired plate. This then gets overwritten in ink and fired with your choice of image in the middle - dishwasher safe, so can be used as a fruitbowl or even just hung on the wall! http://www.allfiredupceramics.co.uk/wedding.htm
have a blanket or quilt on a table and get everyone to sign it. later you can frame it on a wall or put it on your living room couch. another idea is a big piece of barn wood, and a wood carver, and everyone carves their names into the wood. it not only looks neat and rustic, but it lasts a long time to!
we had a blank canvas on which we had drawn ourselves (before the wedding). Our guests were asked to draw them selves and sign their name. We also used small cards decorated in the wedding theme. Our guests wrote a message, and the cards were then used in our (self-arranged) wedding album.
My friends wedding, they had a picture of both the bride and grrom which a friend selected and during the reception each person was asked to leave a little message on the border. Was put in a gorgeous frame and voila! I think its so personal and cute, and they didn't know!