Chelsi,
We used Peat Taylor in Jamaica. He was wonderful and the tour was only $30pp (including admission to the falls). Google his name in quotations and his site will pop up. The tour also included Fern Gully, Wassi Pottery Factory, and a SAFE tour of parts of the island. When school is in session, he also takes the tour to a school (sorry we missed that part). He was an amazing tour guide and I highly recommend him.
We tried to book the Dolphin Discovery independently, but they had no openings. We ended up booking it through the ship, which cost us an additional $24 pp ($75 vs $99). In my opinion, it was well worth it.
I never had a chance to book Stingray City independently (though Capatain Marvin's comes recommended by many of the users of this board). We used the ship to book this tour and Stingray City is a must see.
We walked around Key West, as most passengers did. There were few tours available and none that interested us.
Unfortunately, we were told that Robert, the karaoke host, was getting promoted and would no longer be hosting karaoke. Fortunate for him, not so for the passengers who'll miss his wit and energy. Check out karaoke just in case as we found him quite entertaining.
Know that anything you book through the ship will be more expensive than booking on your own. If nothing else, make sure you use Peat Taylor in Ocho Rios.
Feel free to ask anything else 
