In The Woods... - buy it all. no questions. just do it.
Omnio is a good place to start, since it's a good balance between their later more avantgarde style and is more 'metal' than later releases.
Carpathian Forest is ok, but I personally couldn't really give a fuck about most of it. Go for the early stuff.
edit, I said personally twice right after one another. ok bedtime soon.