Guests are expecting ivory linens, reception location stamped placecards, and a plain book to sign. When you go out of your way to add a special touch to any or all of these elements, guests really remember it.
I recently used individual vases as place cards for a floral spring themed wedding. We pulled all of the different flowers from the bride's bouquet and put them in vases. Not only was it a gorgeous display of 200 vases with the wedding flowers, but the guests got to take them home at the end of the night as a bonus favor!
You could jazz this up in countless ways! Try filling it with foliage for a fall wedding, holly and berries for a winter wedding, sand and seashells for a nautical twist, or coordinating bridal party flowers.