OED 20-volume edition. (1988?)
Webster's New World College Dictionary

Way down the frequency chart after that, a couple of foreign language dictionaries: Langenscheidt for German, Liddell-Scott for Greek, And a cheap college thing for French. Mostly for the German I look it up online at http://dict.tu-chemnitz.de/. Haven't found as useful a French site. I did have occasion to actually look something up in Gesenius-Kautzsch-Cowley the other day, but that happens once very 5 years at most. And the Biblia Hebraica Stuttgartensia is definitely a reference book and not a reading bible.

For reference look-up, the interwebnetspace is definitely taking over from books-on-paper.