I'm a big rollercoaster fan. I've been on the Shockwave in Drayton Manor. I've also been on the Spacemountin in Disneyland Paris, and it's is one AWESOME ride! I've haven't been on much, the main reason is that I've only been to the Drayton Manor theme park only and Disneyland Paris once.
Rita is an interesting one at Alton Towers. The speed at the start is awesome, its like being on a plane as it takes off.
Others that I enjoyed - Incredible Hulk at Islands of Adventure Florida, Aerosmith at MGM Studios Florida, Duelling Dragons Seaworld Florida, Pepsi Max at Blackpool, Air and Nemesis both at Alton Towers.
I love rollercoasters. I always have had a soft stop for Air at Alton Towers, the first rollercoaster of that kind that I ever went on, felt so different to all the others with the way you hang. I was young enough to be impressionable then.
Porta Ventura in Catalonia has a couple of good ones. Dragon Khan is a pretty nippy one on a high track that features 6-8 loops, and the newest one Furious Baco is 0-80mph in no time (3.5 seconds according to wikipedia), the kind of acceleration that you actually feel pass through your body. the start of the ride is literally incredible and the speed is consistent until the final bend over the lake, where it slows down. That makes Baco faster than the Rita, which gets up to 100kph (about 60mph) in similar time.
Shame the wait is about an hour and the ride takes a minute, but that first few seconds nearly makes it worth it. Fastest rollercoaster in Europe atm.