Have some undersea adventures with Lego! See Lego Atlantis!
They have a new line out this spring all about Atlantis. It may be aimed at little kids but there are tons of adults who still enjoy building and creating with legos. I bought the Gateway of the Squid from the new line and it's really neat. If you get a chance check out the details on the squidman! Other neat pieces are the Manta Ray man and the Shark man from other sets. I, of course, have a mermaid (from an older pirate set) and she'll be joining the fish guys in some undersea adventures!
If you're into Lego, there are a lot of older undersea type sets with divers and sharks for you to collect. When I have more room I'd like to make a whole undersea scene complete with ruins and lots of merpeople.
Bricklink. They let sellers sell whatever piece however they want to. Usually it's cheaper than eBay.