I don't know places in the US, but really close to the US is the Dominican Republic. Cabarete is great for kiting. We have apartments at the spot Encuentro and the waves here are fantastic. At Kitebeach you also have flat water. If you want more info, just send me an e-mail (firstname.lastname@example.org) or check our site: http://www.hookedcabarete.com
Florida......You can kite anywhere in the state. The keys has awesome flat water and the East coast has great wave riding. Check out sevensports.com and fksa.org
I was there in November and had a great time.
If you go to the Keys, stop in at Whale Harbor on Islamorada, say "hi" to Brad. He will set you up with compressed air and a launch. He will also let you know about the hot spots in town.
Yes- Florida is a great place to ride in January! Right in the middle of the windy season, and most likely the warmest place (well, with riding!) in the country!
In South Florida you can find some great spots! But, please be aware that there are restrictions in some places, specifically Crandon Park. In order to ride at Crandon:
You must have an IKO or PASA certification card and present it to the Crandon Park office to register as a kiteboarder.
You must wear a helmet.
You must sign in every day you wish to ride (at the Park office) and wear the wristband they will give you.
You must launch and land only in the designated areas (ask any local rider) and stay well away from the beach otherwise.
You may not be on the beach, with your kite in the air, anywhere other than the designated launch area.
It's an awesome spot, and the locals really want to keep it that way!
For other great spots, you can go to kitebeaches.com and check out the postings - from Pompano Beach down to Key West! It's all good!