Boy. Bill & Janice Lozano's Atlantic Kayak Tours has been the place I go for most of my instruction for the last couple of years. Bill is the chairman of the British Canoe Union North America, and their website, particularly the "Expert Center" section, has always been very informative - but I went over there yesterday to get the address to give to someone who had some sea-kayak questions I didn't really have time to answer, and discovered that they've updated it since last I looked. The new setup knocked my booties off - it's so darned simple.
Of course with that out there, I may never write anything again. I have not had time to browse the whole thing, but it looks pretty darned comprehensive - they've more or less got a complete manual of sea kayaking online, with an index categorized by topics.
Anyways, you can check it out here.