Kalmus Beach - Hyannis
So why list this spot? Because I kited here on a windy Friday night and I had a lot of fun. If you are not a very capable kiteboarder who can stay upwind of windsurfers and can control his speed and direction of travel perfectly don't even think of kiteboarding at this beach. You will be lynched by the local windsurfers. West Dennis Beach is a much better beach at which to perfect your kiteboarding skills.
There is a public beach (Keyes Memorial) right up the coast from Kalmus. We also launched at this beach after the lifeguards left. The wind is more sideshore and you don't have to deal with the windsurfing traffic. Regardless of where you launch, don't kiteboard if you can't do it safely away from beachgoers and windsurfers - it is not worth the risk!
Directions: From US 6 use exit 6. Travel down SR 132. At the rotary exit onto Hyannis-Barnstable Rd. Turn right onto Main St. Make a quick left onto Ocean St. Before Ocean St. runs into the ocean turn left into the Kalmus Beach Park. Parking is $10/day.