I've heard Concealed and loved it. I usually don't like technical death metal, but Augury actually write really catchy and epic tunes.
Quintessence. "Colossus" is a fantastic song though.
I love Empiricism, but it seems to be shunned by most Borknagar fans.
That said, The Olden Domain has risen to the top of the list for me. I used to love Quintessence the most, but the pagan/folk aspect of The Olden Domain and Garm's vocals have steadily increased its level. I can listen to the entire thing without ever feeling bored or skipping a track.