Bahia Salinas, Costa Rica
Bahia Salinas and especially Playa Copal is a great destination for kiteboarding if you're looking for strong winds and flat water. Even though the place is a bit remote, in the northern west part of Costa Rica, towards the border with Nicaragua, it is still easily accessible by car and it has plenty of accommodations, food and entertainment.
We went there for a day in February, 2013 while doing a tour of Costa Rica and the place was blasting with 30-35 knots wind side-on gusting to 40-45. Everyone was riding 5 and 6 meter kites the whole time.
We spoke to Damien, from Kiteboarding Costa Rica and found out that during the months of December, January and February the place is nuking with strong winds. The location is pretty gusty, so we recommend a kite that can handle strong gusts if your bring your gear with you. If you don't you can always rent from the guys at Kiteboarding Costa Rica for a very reasonable price. We paid $60/day and had a whole selection of brand new Cabrinha kites, boards, harnesses to choose from.
If you're planning a trip to Central America and want to kite while you're there, we highly recommend Bahia Salinas for its strong winds and flat water. Be warned though, it can get very gusty when the winds are strong.