The lobster buoy hitch is a fast, secure knot that I find myself using in almost any instance where a rope must be fastened to a post, railing, tree branch, or ring. It works well as the "fixed end" of a rope, like a clothing line, where the opposite end is attached with a taut-line hitch, for adjusting tension. The lobster buoy hitch gets its name from the commercial fisherman who use it to tie off their pot strings and buoy markers. Though it first appears somewhat bulky and pretzelesque, this knot compacts well once tightened, and is very strong. Unfortunately, it can jam (especially with certain types of cordage), but in most cases is fairly easy to untie, even after bearing a heavy load. I also use my own "slip" variation, where the working end is formed into a bight before making the last pass through the hitch loop. The knot then remains secure under load, but can be released much faster by pulling the tail of the slip, which collapses the knot. I wouldn't recommend the slip variant for any critical load, but it works quite well for most applications. Here is the lobster buoy hitch:
The Rope People also provide a useful animation of this knot.
View it HERE.