I think we all know that a roller coaster doesn't necessarily have to be big to be a great ride. There are plenty of coasters out there that are less than 100 feet tall but pack a good punch. For me, my favorite under 100 foot coaster would be Renegade at Valleyfair. It has a great S-shaped drop, several nice moments of air, and is out-of-control. It stays close to the ground most of the time, which makes it feel faster than it really is. I probably feel a little soft for it since it's at my home park, but it's still a great ride. I give honorable mentions to Spongebob at Nickelodeon Universe and Ozark Wildcat at Celebration City. Even though Spongebob has been getting slightly rougher lately (as I mentioned in my recent trip report), it still packs a great punch for being only 75 feet tall. I rode Ozark Wildcat almost 11 years ago, so I don't remember that much about it, but I remember it being a very fun ride. I hope that this ride can be saved someday.
Renegade
Spongebob
Ozark Wildcat