i'll second Mongoose's Seas of Blood. it's the only one that i own, however. i like its method of designing ship stats, as well as its naval combat system.
i thumbed through the Seafarer's Handbook at my FLGS, and it looked like it spent a lot of space talking about the underwater environment, which i have no use for in my campaign. of course, that was just from a preliminary skimming -- someone who actually owns the book could probably give a better summary.