I used to love Puerto Viejo (southeast coast, almost to Panama) and the laid back atmosphere. Like BlueDevil said, it is definitely a more rasta kind of lifestyle. However, the crime in that area has really been a big problem the last year or two with hotel invasions, robberies, murders and a lot of other stuff that has forced me to no longer recommend that area for travel. Biggest problems two years ago were the lack of hotels with air conditioning...
It is really too bad because Puerto Viejo has some of the best beaches in Costa Rica, namely Punta Uva and Playa Grande where the road comes to an end. There were also some neat places to eat and a decent nightlife. The place didn't have much P4P for guys but was known to be an area where women could go to 'rent a rasta'.
One of the best 'tours' in the country, in my opinion, was with the Bribri Indian Tribe reservation (
http://en.wikipedia.org/wiki/Bribri_people). You traveled to just west of the town of Bribri on a dirt road to a trading outpost on the river that is the Panama/Costa Rica border. The Indians would then pick you up in a canoe for the trip up the river to their reservation. You could then spend as many nights as you liked with them, learning about their culture, how they live, hunt and survive in a jungle wilderness. Was quite fascinating...
The Limon area (central east coast) is also a high-crime area. Costa Rica has a hard time finding enough police, doctors and nurses to staff it because no one wants to live/work there. There isn't any really good beaches, sights or really anything else to attract you to that area.
The northeast coast is basically a swamp. The only town is Tortuguero and the only way to get to it is to take a boat from Cariari or fly in from San Jose. It is a beautiful area, low crime and some fantastic wildlife including nesting turtles. Have had many friends travel there and all loved it but due to the remoteness, it is expensive to get to and stay there.
If you want to see a place in Costa Rica with a 'counter-culture' feel but is a bit more safe, I'd recommend Montezuma on the Nicoya Peninsula.