For my sister's wedding, everyone received an helium-filled balloon and a postcard. On the postcard, we had to write the address of the newly weds, our name, and the name of an object we committed to offer to the couple if the card got back to them. Some ideas were really nice ("voucher for a trip in a balloon", "voucher for a total relooking of the groom", "voucher for a diner made by my children",...) and the balloons release was beautiful. Now we hust have to wait for the result !