A "wishing tree" is a traditional part of Dutch weddings, and an interesting alternative to the guest book. A beautifully shaped bare branch (or two) is placed in a pot and arranged on a table beside the bride and groom's table. The branch can be bursting into bud for a spring wedding, or a dried and painted branch. You can decorate the branch with ribbons or beads, whatever looks beautiful to you.
Guests are given a paper leaf or piece of decorative card attached to a ribbon when they arrive. During the reception, they write their best wishes to the bride and groom. The couple gets to read them before hanging them on the branch. After the wedding, the couple can use the branch as a centerpiece or decorative item in their own home. Eventually, couple can take the leaves/cards off the tree and make a collage of them or put them in a scrapbook. Whatever you do with it, you'll have a tree-full of warm wishes to savor for years to come.