The one tool that you simply cannot be without is the NL track packager. If you don't have it already, you really need it.
AHG is a must for Intamins, B&M's, and GCII woodies. It will save you tons of time and make heartlining coasters really easy. I also reccomend getting a copy of buster's track smoother, which is a nice way to get rid of some of the little bumps in the track. Finally, you'll want an object creator. I reccommend Tia's 'object creator', because it is so easy, but Anim8or is also a great tool if you are willing to take the time to learn it. I'll admit that Elementary is also a good tool, even though I don't use it personally.
So:
-NL Track Packager
-Automatic Heartline Generator
-buster's "Track Smoother"
-"Object Creator" or "Anim8or"
-"Elementary" (depending on if you want to design coasters using math or manual labor.)