I practiced on two Waters Dancing kayak kits, a Lightning 12 and 14, and then built a 16' balanced lug yawl from Campion Sail and design: http://www.campionboats.co.uk/
I really recommend the boats, one of many to choose from, from 11' to 19'. Tom Dunderdale is very helpful with information and tips as you build, and has a lot of experience with small sailing boats. Not for those who haven't built anything before, but neither are any of the designs others have mentioned.

Also take a look at http://www.selway-fisher.com/index.htm

If you haven't built anything and/or are in a hurry and want to keep it simple try one of Jim Michalak's designs:http://www.duckworksbbs.com/plans/jim/michalak.htm.
Good luck

Peter Lord