If you are looking for a nice beach, Nagril has the best in Jamaica. Like Stoner said, though, the night life is pretty tame...well, I think it was. My husband and I went there for our Honeymoon and pretty much were pooped by 10pm...which is odd for us because we are both night owls and never go to bed before 2 or 3 am. But we were up early...8am or so for the first dive of the day and between that and swimming and drinking and the sun, we were beat!
From what I have been reading on these forums, Jamaica as a whole is rather laid back. You should look into Cancun...the nightlife there is better...but just don't go between mid Jan and Easter because that is spring break time and so you will be surrounded by kids. Good luck with your wedding and honeymoon!!!!!!!!