It would be helpful to know exactly where you've gone before but I'll give it a shot:
1. Half Moon Beach - it's located about 10 minutes from the beach in Negril and is an AWESOME alternative to the busy beach at Long Bay. They've got a great little restaurant and bar there, and the beach is kept natural. It's the local's choice for some beach R&R. Its my favorite beach in the area, we're there just about every Sunday when I'm on island.
2. Zimbali Retreats - On New Canaan Road just outside of Little London. Its a large organic farm and the hosts are happy to give you a tour. You can even book some time with a Rasta Naturist.
3. Venture River aka Steve's Aqua Park - a nice alternative to Roaring River if you've been there already, its a bit more off the beaten path and less touristy. Lovely grounds and swimming hole.
4. Abeokuta - Its an old plantation with "ruins" from structures there that date back 300-400 years. The large mineral spring fed swimming pool is the oldest in Jamaica (300-400 years old).

Have fun!