I have Property in Costa Rica, and i again echo the sentiments about Jaco. It is really gone to shit. It is also the one of the busiest times of the year. What are you looking for? I love Dominical but it is 3.5 hours from the Airport, so that may be rough for a weekend outing, unless you get a puddle jumper to Quepos or Palmar Norte. Check out Nature Air and Sansa for information. As far as whitewater, Turrialba is the capital, but it is hours in the wrong direction. If you head to Quepos or Dominical Hit the General in San Isidro Class IV and amazing, or the Guabo it is a really nice classe 3 float with a 5 thrown in for fun. There is lots of Whitwater down south so either pick up a copy of Chasing Jaguars by Lee Eudy or hook up with a guide. There is a good one in Dominical; its called Dominical Surf and Adventures, they are a great couple that are service forward.
So, post what you are looking for. I would love to help you out any way I can. I have a lot of good connections in Costa Rica. But there is a lot of Country to Explore. Remeber that it is a country the size of West Virgina that has 8 recognized climate Zones. It is also "summer" break for the kiddo's until Easter, so it will be busy on the beaches...