Prior to arriving in Belize, I tried to book a custom trip to Tikal through them, and had a lot of trouble communicating with them because I did not want to book the typical 1 night tour, staying in Flores. Ended up booking it through Katie at Maya Travel, who you can link to through this site.
But, once I was at Banana Beach, they were excellent! Highly recommend Sandra (who is also the star of the Belikin calendar). She spent an hour looking all over the hotel for me when she was able to book me on a last minute snorkel trip (she was having trouble reaching Alphonse, the guide). You can probably book directly through the tour operators and pay a little less, but Monkey Business makes everything convenient - and when I had to cancel a snorkel trip due to slight case of turista, Sandra handled all the logistics.