Are you visiting only one park? I ask because Disney has spread out their thrill rides amongst all 4 parks, so to really experience them all you'd need more than one day, or a park hopper pass. Yes, you can hit all of the thrill rides in one day with a park hopper! It probably isn't possible in an exceptionally crowded time like Christmas, but it's definitely possible in June (ask me how I know!)
If one park it must be, I'd recommend Disney's Hollywood Studios.
-Rock N Rollercoaster can't be beat for big thrills. 0 to 60 mph in 2.2 seconds - WOW! Check it out
here.
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Twilight Zone Tower of Terror - need I say more?
And while they're not exactly 'thrill rides', The Lights, Motors, Action! Extreme Stunt Show is very thrilling, and the brand new Toy Story Mania ride, while quite tame, is a LOT of fun!
If you are able to visit the other parks, then I'd recommend Mission: SPACE, Test Track, and Soarin' all in Epcot, Expedition Everest and Kali River Rapids in Animal Kingdom, and Space Mountain, Splash Mountain, and Big Thunder Mountain in the Magic Kingdom. They are all great rides, but do keep in mind that none have the huge impact that Rock N Rollercoaster does, so set your expectations accordingly. :)
Have a great vacation!