Pile Hitch
This is a convenient hitch when you have access to the end of the post. If you need a more secure hitch, you can make it a Double Pile Hitch by spiraling down the post an extra 360 degrees with the bight of rope before throwing the bight loop over the top of the post.
The way this hitch is made also makes it an ideal hitch for hitching at the middle of a rope.