Trailer Sailor Board: the best messageboard on the internet!
Super Sailmakers... the manufacturers of Seaward Sails
Bob Hornett's Trailer Sailing page... He has a San Juan 21, good links to many sites
Dinghy and Small Sailboat Cruising... alternative crusiers and great links
Serendipity...everything you need to know about small yacht cruising
(A good resource of info about various designs, as well as a good source of used boats if you live in the midwest)