For my money, Natural Born Chaos is a great starting point. They are thrashier going backwards from there, and a bit more melodic going forward. Also, Devin Townsend produced it, and you can tell. Most of their stuff is great (and their current drummer is better) but to me it's the best snapshot of what the band is all about. Most memorable songwriting as well. After that, if you want to go more proggy, definitely The Panic Broadcast. Stabbing the Drama and Sworn to a Great Divide are a little more mainstream, but still really, really good.