2000 YZ125 and a 1990 CR125.
Dirtbikes are a great way to have fun and learn about sliding the rear (or front), power wheelies out of corners, and all that fun stuff without really worrying about dropping it. They're simple to work on, the first bike I had apart was a '93 KX80 on which I was able to completely assemble the engine with only a Haynes manual to guide me (I didn't have the privilege of taking it apart first, it was a basket-case). Last saturday I just finished building a ramp for my bike, I'm working up the speed a bit, but so far have gotten about 10' air/40' distance off of it. Do yourself a favor and drop a bit of green and buy the gear, at least helmet/goggles/boots/gloves. They've saved my butt more than a few times. Work boots are ok if you're not jumping, combat type boots with a steel shank wouldn't be bad at all.