Here's a few pointers:
Fujiyama (Fujikyu Highland Park) - in '97 was the tallest, fastest in the world and is still an impressive, smooth, fast and fun beast. Highly recommended.
Dodonpa (same park) - new this year, and claiming to be the fastest. It starts on the horizontal and blasts off from 0 > 178 km/h in 1.8 seconds. An amazing rush. Then goes up (at 90 deg) and down (at 90 deg) a small "hill" and that's it. Something youve never felt before.
Suzuka circuit (Mie Pref) - they have a couple of decent coasters.
And I have heard that the most recent "tallest, fast