The Cow Hitch
Ok, maybe not the strongest or most useful of knots (especially for those of us who don't own cows), but its symmetry and simplicity makes it a rather handsome little knot. It's also pretty easy to learn and can be tied in a matter of seconds.
Knot Video: How to Tie the Cow Hitch Knot
Knot Tying Instructions
Step 1 - Wrap your rope around a pole, post, tree trunk (or whatever), and cross the short end under the main running line (the other end of your rope should be hitched to your cow, or other subservient quadraped).
Step 2 - Bring the short end up vertically.
Step 3 - Wrap it around the back of the pole.
Step 4 - Insert it through the front loop you just created, running along the top of the main line and pull to tighten.