I've stayed at Mopan River Resort. Since I was there, Pam and Jay have added a pool and a wedding chapel.
I think it's really nice, with beautiful "upscale thatch cabanas" and one of the best values in Belize, since everything is included even down to taxes and tips and tours and transfers.
They've got it set up so you can do all the basic tours on a week's stay. Obviously weather can play a factor in scheduling of the tours.
Of course this kind of place is not for everyone -- some people want more independence and the chance to go where they want on whim. Also, keep in mind this is not really a jungle lodge. It's right across the Mopan river from "Old Benque" though the grounds themselves are beautiful.
An added plus: Jay can give you tax advice!
--Lan Sluder www.belizefirst.com