I have known this one for a long time, but I did a search and did not see it in the forums. So, I figured I would post it. If there are any large cliffs or hills that you want to travel down but would normally die; walking down these hills backwards will prevent you from falling.
This trick is very helpful when being chased by mobs, because they will reset pretty much every time. Also, it is humorous when being chased by players because many of them will jump right off the cliff and die.