A great place to start would be their Dark & Long EP, the 6-track one with Thing in a Book. You might be able to find it on eBay like I did.
Right now all I could find was
this one going for AU $35.00 which is ridiculous
I think I got mine for somewhere around 8 bucks.
It has a bunch of tracks you probably haven't heard yet, and it's one of my favorite EPs of theirs. Excellent stuff.