Marinews Boating
Covers common boating knots including the Cleat wind, Clove hitch, and Wagoner's hitch. Animations and common uses.

Shooting Star's Marlinspike Page
Covers common boating knots including the Anchor bend, the Carrick bend, the Buntline hitch, and several variations of the Bowline. Animated illustrations and step-by-step instructions. Table showing the relative strength of the knots.

Boating Knots
Covers several knots commonly used in boating.

Uspowerboating.com: Boating Knots
Pictures and videos of a great variety.

Boating Magazine
Pictures and instructions on how to tie a few knots.