This is my top 3:
1. Beach and National Park
I recommend Manuel Antonio: http://www.manuelantoniopark.com/mapk/de...
and Corcovado tours:http://www.laleonaecolodge.com/costa-ric...
2. Volcanos
3. Costa Rica Sport Fishing:
http://www.cristalazul.com/sport-fishing...
Costa Rica is amazing, you'll love it!
You don't really say how much time and what you are interested in. The time you have available is crucial. The normal itinerary includes rainforest, volcanoes and beach with time pretty evenly split between the three. However, wherever you go depends on time and interests for example if you have two weeks or more Corcovado would be a great rainforest option but if you are spending less than 10 days in the country it would not be.
Try national parks, places like Manuel Antonio, nice hotels that offer you relaxing environments, like http://www.sicomono.com and you won't be disappointed of your visit.
