Faller makes models of coasters. I wouldn't consider them toys or even for beginner model makers though. They have tons of tiny parts a are fairly expensive ($150 or cheaper on Ebay). They also make many other rides as well including bumper cars, log flume, and a few spin and pukes.
www.walthers.com I think if you look under circuis items you can find the rides.
There is a another kit you can build coaster like layouts with using plastic tubes and steel marbels. You can build loops and other layouts although the marbels loose speed fairly quick. I had one of these about 10 years ago. don't know if they still make em though.
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2000 stats: 135 coasters in 26 parks
Not Too Shabby For A Summer