There's horseback back riding at Happy Trails Stable. Look on www.bahamasgo.com, then click on the Eco link.
A lot of other posters have recommended the Stuart's Cove trip where you can snorkel and watch the shark feeding beneath you. I'm sure someone else can fill you in on that one. There's the Powerboat adventures trip, which is an excursion to Exuma: www.powerboatadventures.com.
Of course there's Atlantis, which I think everyone should visit. Shop, eat or just walk around. It's very beautiful. I'm not too sure about nightclubs, but when we went, we were told to checkout the Zoo or Club 601? I'm not sure which is better, but I heard the Zoo is a little wilder. Can't speak from experience though.
Also look on www.majesticholidays.com for excursions and city tours. There is so much to do in the Bahamas, I really don't see how anyone could be bored or disappointed. Don't forget to ask your hotel staff for suggestions too. Have a great time!!