River rocks. Have a bowl of rocks for your guests to sign with fun (metallic, colorful) pens. Then, place in a large hurricane jar on your coffee table to display year after year.
This reminds me of another tradition Jordan and I've already started. We save our wine corks (an idea from Mom) - we write on the cork everytime we have a bottle of wine. Even if it's just dinner at home. We have them saved in a hurricane jar and every now and then I go through and read them. It's a great reminder of what we've shared together, memories of eachother, friends, and family.
Another idea that I adore. Have guests sign squares of fabric and make into a quilt. This reminds me of grams. I am not a sewer (maybe I'll register for a sewing machine), but Jordan's Mom, Cindy is a great seamstress and I would love for her to put the quilt together as a wedding gift! Definitely something Jordan and I would cherish!
And finally. A guest book tree. Jordan has a love for trees. Place blank tags (or decorate yourself) and have guests sign them, and hang on a "tree". To make, use manzanita branches and place in buckets. So cute. And I know Jordan would love this.