Obviously the most common save is the protecting a 1, 2, or 3 run lead variety. Still counts as a save if the pitcher gets his team out of the 8th inning, and they go on to put up 5 more runs in the next frame... if he finishes up in the 9th, he is still awarded the save.
It is also a save opportunity if in the 9th inning (or the 8th and then finished in the 9th) the tying run reaches the on-deck circle. So coming into a 4-run lead game with two base runners on OR a 5-run lead with the bases loaded constitutes a save chance.
/end Saves 101