Things you gotta see (that I did see)

• Volcan Arenal -- active volcano, everyone's gotta see this. Stay in 'La Fortuna' it's a great little town at the base
• Manuel Antonio -- awesome beach, near San Jose, great place to start. try the surfing, you might perish in those monster waves

off the beaten path:

• Corcovado Nat'l Park, Penninusla Osa -- amazing. crazy animals, beach hiking, tapirs. you gotta go if you have time, it's not the most common destination and it's a pain in the ass to get to. you will likely have to rent a 4x4 and drive there, find a guide. we met a waiter that took us in there and it worked out great.

Other places i wish to go sometime but have no barometer on:

• Guanacaste Province -- far west of the country, heard there are great beaches there
• Monteverde Cloud Forest -- one of my friends went there and loved it. you take a jeep-boat-jeep thing across a lake to get there i think
• Totruguero -- where the sea turtles swim up and lay their eggs. protect them from poachers

the only places I heard that were somewhat unsafe (crime/unfriendly) were San Jose's less traveled parts and Puerto Limon.