The Moon & Antarctica is a must. i might be biased since i first heard them live on this tour, but it's really very good. it also marks the beginnings of their progression towards more accessible sounds, so it's kind of in between.
for earlier stuff, check out This Is A Long Drive For Someone With Nothing To Think About. it's my favorite
but really, you can't go wrong with any disc you pick up. they're all worth listening to.