My friends Shelly and Paul are getting married in a few months and they registered with Honey Fund to literally fund their honey moon to Tahiti. It's a great free way to register for gifts or money for a wedding.
Using the Honey Fund makes it more personal than simply sending the couple a check or some cash because each item or excursion they would like is itemized; a romantic dinner, a boat trip to another island, scooter rentals, a show, even the plane tickets, are all listed as gift items. The fund even makes it possible to buy just a portion of a big ticket item (like the plane fare), so you can contribute as little or as much as you would like without paying for the entire item. At "checkout" you can either pay through Paypal or print out a gift receipt and enclose your check or cash with the receipt showing what you have bought the couple.
Of course the Honey Fund also allows the usual gift registry at brand name stores like Crate and Barrel where tangible items are listed and you can buy them (and have them shipped) for the couple. But as my friends said in their announcement, there isn't much they need now or can fit into their small place, so helping them fund their Honeymoon would be much more practical (and fun).
Having been to Bora Bora alone, I know it is much better to travel there as a couple, and it's even better to travel there on a honeymoon with all expenses paid.