Mid tower is usually under 19" tall
Full tower is around 24" tall
Super mid goes up to about 21"
You may also get more depth and width with the bigger cases too.
.bh.
Oh, and there are cases beyond 24" tall, I guess they'd have to be called Monster Towers. .bh.
And I agree with JBDan, I saw a "full tower" recently while browsing cases on the Egg for around $30 or 40. + shipping w/o PSU (might have been an AMS). As I recall though, it didn't have much going for it except height.