I thought this was a useful article (to someone as ignorant on the matter as me):
http://en.wikipedia.org/wiki/OBD-II_PIDs
The enginelink software will let you load PIDs for a small number of specific cars.
I notice the reader doesn't turn off with the engine. Guess I,ll have to remember to unplug.
EDIT: Ok, I just noticed someone beat me to the wiki page. This won't be an uncommon thing; I'm the quintessential absent minded professor (well, scientist).