We are often asked about boat plans. We don't offer any plans ourselves, but listed here are a number of designers and collections of free plans available online.
When looking for boat plans, it is a good idea to set up some selection criteria first. How many people should the boat carry? Is it to be purely for rowing, sailing, motoring, or a combination of some of these? Boats suitable for rivers and sheltered estuaries probably won't be suitable for the open sea, and good deep water boats may not be suitable for exploring shallow creeks and backwaters.
Find out about the sort of support a designer offers, if there are online forums where you can talk to builders of the design you are interested in, and ask others for their opinion about a design, and about the reputation of the designer.
With the above advice in mind, the sites listed below, in no particular order, will be a good starting point when looking for plans online:
Michael Storer Wooden Boat Plans
Free woodworking plans - boats
Bateau (check out their free plans as well)