LaurieMar;
Sorry, don't know a decent website, but have some first hand knowledge.
I spent a month in Costa Rica in 1997 and spent time on both the Caribbean and Pacific side. While the pacific side is long, endless sandy beaches (both white and black sand depending where you are), the Caribbean side is quite diverse.
Up north close to Nicaragua is the area of Tortugera. It is only accessible by boat as it is a series of waterways, etc. This is where the "jungle lodges" are and a real opportunity to see a lot of "wildlife" (howler monkeys, toucans, crocs, etc.). I don't know how things are organized now, but in 1997, it was a lot easier to get to Tortugera by joining a tour. Not my preferred way of travelling, but I have to tell you that it was worth it. Fortunately, we were in a small group of 7, all around the same age group.
South of Limon is a wee place called Cahuita (Ca-wee-ta) on the ocean. There is very much a Jamacian influence present given the proximity between CR and Jam. I stayed at a place called the Atlantida Lodge. The Cahuita national park has great pathways bordering the ocean on one side and jungle on the other. There is some good snorkeling locally.
The roads all over CR are not great. Big potholes the size of craters! It is easy to get around whether you take public transportation or rent a vehicle. My friend and I just got airfare and booked our first night at a hotel in San Jose. From there, we just winged it. Ecotourism is their bread and butter, so finding out information and hooking up on excursions is easy.
On the pacific side, I spent some time in Tamarindo (more north) and in Manual Antonio (more south).
The people are very friendly and helpful, the food delicious, and the environment enchanting. As two single women travelling around, we never felt unsafe. Even the different bathrooms we came across were ok. (Something important to us women!)
I agree with the others, the country is extremely diverse in its makeup and there is so much to do if that's your cup of tea. We went hiking up the side of Arenal volcano, horseback riding, white water rafting, canoeing through the jungle and lots of R&R/beach time. I enjoyed my time in CR. I can't comment on differences between CR and Belize, as I've only been to Ambergris Caye (for a month this past Jan/Feb). I would go back to either place, but as San Pedro is so fresh in my mind....I am leaning more towards Belize as my fav! My husband and I had an awesome time in SP.
Hope this is helpful.
Cheers