Bookshelf speakers installed on the bulkheads where the chainplates are.
I had to install a 40 watt booster though as the stereo didn't have enough grunt to get over the sail luffing noise (in 25 knot winds)... heheheh... now everyone can here my Knightrider theme song, and of course the Jeffersons! hehehe... My stereo has a flash card no CD drive... works great. Also am using an XM portable for the boat, and works great.
The bookshelf speakers are decent sounding, and were $19 for the pair (buy.com). No bass but of course that's to be expected.