Almost as fun but not nearly as destructive is the wet decaying leaves skid. We have had some major leaf blow-downs in the past couple days, followed by rain. This makes for a combo slicker than snot and conveniently located in the shoulders of most roads.
You really have to watch your balance though, as the stuff is so slick that your rear end will start to slide out very easily. I was able to execute a perfect bmx-style skid stop on this stuff just yesterday. Problem is, it was an accident.
Try it. Its fun.