We did a tour to see the butterflies and birds...and it was a very fun tour.
A lot of people book with Victor Bodden tours Victor Bodden - Bodden Tours - Roatan Tours and Roatan Excursions - Roatan Honduras
where you can get several tours, including a visit to the monkeys. Prices seem pretty reasonable starting at $40 per person.
The big negative, is you have to walk out of the Cruise Terminal to meet your tours, so be prepared for some walking.