Double Bowline
Do not confuse this loop with a Water Bowline.  While the Double Bowline is certainly more secure than a standard Bowline, it typically isn't quite as secure as some other end loops like the Water Bowline or the Zeppelin Loop.  However, it is easily adjusted and won't jam.

you don't have to, this is the one Bowline-type loop that I find easier to tie the landlubber way (as shown) instead of using the one hand twist method that is advantageous for the Bowline and Water Bowline. 

Beware of "add-ons" that are purported to add to the security of this loop.  They often add surprisingly little to the security of the Double Bowline while just consuming rope and lending to a false sense of safety.  Rather than assuming your knot in slippery rope will stay tied when being mercilessly wind-whipped,
test it.