I know it's typically ranked fairly high, but one of my top 10 that doesn't get talked about alot is Volcano at KD. And Dominator as well as someone said earlier. I think KD has a pretty solid lineup that has gotten alot better with Dominator and I305.
I'll go with Kennywood's Jack Rabbit. The double dip still has its charm almost a century later, and the ride holds up much better than a lot of newer woodies (including the whiplashing Thunderbolt).
*Fear is the mind-killer. I will face my fear; I will let it pass through me.*
Daemonen @ Tivoli Gardens. I wouldn't say it's underrated, per se, but at least under-appreciated. I honestly don't know what the general opinion of it is. All I know is that I rarely see it mentioned, but I loved it when I rode it.
I'm one venturing to say Mean Streak. I hear SO MUCH negativity about that ride. Come on, really? It's not THAT bad. And it doesn't rattle you around to the point of breaking your bones, folks. Idk, I guess I'm kinda biasing this opinion by the aesthetic impression this coaster seems to give me. Seems to have quite a magnificent looking structure. Pretty visually appealing.
I personally don't hate it's because it's bumpy. I hate it because it's boring. And it's really starting to lose its aesthetic appeal as well. Not nearly as pretty as it used to be. Wood ages, I suppose.