So lets say you don't want to do a charity registry, but you still want to use your wedding as a cause for good. If you live in the area and are interested in a waterfront wedding on the bay, check out the Chesapeake Bay Foundation's Philip Merrill Environmental Center. It's a good way to support the CBF and have a beautiful wedding. CBF is a little out of our budget (<$4,000), so we haven't looked at it, but if we were dead set on a waterfront wedding, this might be the way to go - you aren't locked in to your own caterer, the way you would be at Celebrations, Chesapeake Bay Beach Club, or Herrington. And the space and the view are absolutely beautiful. And to be as "green" as possible, you get to have the ceremony and reception in the same location - the rental includes the beautiful deck, as well as an indoor space that has a ton of windows.
(And in case you also find the PMC to be a bit cha-ching, but are donating in your guests honor to the CBF and are hoping for a cute favor donation card idea? Crab shaped candies in cellophane bags with a treat tag folded over the top. Or candles shaped like crabs.)