In my life béfore being such buzzzy with CG, I was a really enthousiastic themapark / coasterfan, so I know some really cool refs! (I’m still a coasterfan; I’ve a seasonpass for ‘de Efteling’, and I am quit active on www.themepark.nl , a Dutch themeparkfanclub 
. Few years ago I also built a (sort of) coaster my backyard! >> www.oldentower.tk )
http://www.rcdb.com/
The ‘Roller Coaster DataBase’, with info of really áll coasters around the globe!
http://www.nolimitscoaster.com/
Nolimits is a coastersimulation program, in witch you can build (Nolimits editor) a rollercoaster in total 3D, and after that ride it (Nolimits simulation)! It the best simulator in the market, and its also often used at the designing stage of a rollercoaster. If you need some inspiration for how the movement is and so, it’d be nice to use…! (you can download a free demo)
http://www.coastersandmore.de/indexe.shtml
Coasterandmore is available in English or Deutsch. Its stunning informative about all kinds of coasters, and the techniques used in it!
http://www.skillreactor.org/cgi-bin/index.pl?rolcoast
Making a rollercoaster in Max (not really good, but maybe you can use it)
[I know there wás a very cool site with some 3D coasters (really detailed etc!), but I cant find it now 
… Maybe I’ll add it later.]
-edit- I found that site!:
http://badnitrus.coasterbuzz.com/
Awesome site with 3D-pics of allot rollercoaster. You can get as wel layout ideas by this, as some inspiration to how build a coaster. Excepting pics, there are also movies!
[edit] I added a list with some links to some rollercoasterproducers:
http://www.vekoma.com/
Vekoma is the best known coasterbuilder on earth; a Dutch compagny that built allot good and nice rollercoasters!
http://www.intaminworldwide.com/
Intamin has some really cool rides; not only rollercoasters but also waterrides (what doesn’t matter to you I think; you got to built a coaster ). They have very beautiful hypercoasters; very tall ones (like in the pic above)
http://www.mack-rides.com/en/index.php
The site isn’t up right now, but it deserves a place right under the other producers. Check some of their coasters out via Google, or so
Bolliger-Mabillard [B&M][they don’t have an official site yet ]
They build the most awesome and most beautiful rides on earth, in my eyes! Very tall, and robust! People from the VS will regonize this ‘style’ of building maybe; there are állot B&M coasters in the VS (in the Six Flags-parcs for example; also in Universal’s World of Adventures’ )!
I hope you’ll use something of my links…!
I wish you good luck @ the challenge!
Greetz, Gijs
. Few years ago I also built a (sort of) coaster my backyard! >> 
… Maybe I’ll add it later.]