I'm jealous!
We stayed with these guys and they took us everywhere we wanted to go, twice a day, packed lunch, beer, drove, watched our stuff, took pictures, etc.
http://www.witchsrocksurfcamp.com/ The Witches/Ollies point boat ride (playa del coco) is a must, and if you can afford it, and the winds aren't too strong (the popagayos can blow too hard offshore to even surf), just do that every day. The other breaks are good, but Ollies and Witches are just insanely good.
The surf is usually pretty small in Tamarindo itself, but directly north of it is Playa Grande, which can be an awsome beach break when it's on. I've gotten some of the best barrels of my life there. I think you can actually walk to it, if you cross the river on the beach at the north end of town... otherwise, it's about a 20 minute drive because you have to drive inland to find the nearest bridge.
Oh, and if you're inclined to do some travelling, the best surf in the region can be found just to the north of Costa Rica, in Nicaragua. Hit up these guys for tours there:
http://www.quiksilvertravel.com/nicaragua/ Eberly's an old shaper dude from North County San Diego, and he's got a pretty good crew. We like them alot.