If anyone is interested in a trip to the mainland to see wildlife and the Mayan ruins I really recommend Daniel Nuñez. We took an all day trip up the Old River and to Altan Ha. He was one of the best naturalists we have ever encountered. He had an eagle eye for spotting wildlife and was very knowledgeable.
We saw dolphins, manatees, all sorts of iguanas, crocodiles and an amazing assortment of birds.
At Altan Ha he was our guide and again he really knew his stuff about the site. We climbed to the top of one of the ruins and while walking around the site he continued to spot some amazing birds.
The trip was a bit pricey, but we thought it was well worth it. The price includes everything -- entrance fees, a nice lunch, drinks, beer, rum punch, etc.
His web site is: www.tanishatours.com
By the way thanks to all on this message board. It was a great resource for planning our trip!