Along with a standard hitch (not shown here), these are the 2 knots I find the most useful for docking boats. They're also useful for non-boat purposes. The clothesline is great for any light load that needs to stay taut. It is adjustable. So it's great as people get on or off the boat. As fat people get on, you can loosen the knot. As fat people get off, you can tighten the knot and keep the boat toward the wall.
The bowline is perhaps the single best knot period (if such a thing can be said). It makes a loop and then ties to itself (as opposed to hitch that ties to the object). Loops are great because you can do so much with them. Attach 2 lines to make one longer line. Make foot holders to climb up a wall. Drag dead bodies out of artic depths. And tie up a boat. This knot won't come undone, or "capsize," as they say in the knot business.
Good website at http://www.netknots.com/html/boating_knots.html
Imagine the boat on the left and the shore on the right. This is the sliding tautline hitch.