Sawfish Bay Park has a good launch site (not a boat ramp) on the Intracoastal. The Intracoastal Waterway has a no wake zone for boats in this immediate area. Parking is free but the port-a-john is scary so take care of those needs before you arrive.
There are 2 islands just across from the launch to explore; Bird Island and Fullerton Island. Fullerton Island is part of a restoration project with the Palm Beach County Environmental Resources Management started in the summer of 2013 and should be finished by the summer of 2014. Once completed Fullerton Island will be like a smaller version of Munyon Island which is further south in the Intracoastal, complete with mangrove channels that will be navigable by kayak or SUP and a boat dock for day use. It will be nice to see it now before the restoration (first picture below) and when it's finished next summer (picture at the bottom). Paddleboard rentals will be available through our sponsor, Paddleboard Connection, for $30. Please let me know that you will need a rental board(s) when you RSVP. See you on the water in Jupiter!
UPDATE: I hear that the lagoon within Fullerton Island may be open so we will check it out. There is definitely progress being made on this restoration project!