Simply the only dictionary that matters.
Big words. Small words. Name a word... it is in here. Even my last name counts as a word in the English language. I've never heard it used in conversation, but "trendl" is in there with plenty of variant meanings and literary references.
It isn't for everyone. Who needs a huge multi-volume dictionary... keeping in mind multi means what multi should mean... many? However, for those days when TV is a drag, NPR seems like the same old shows rescripted and you just don't feel like doing anything... browse, browse, browse!
Get lost in the incidental words of the English language. Look up one word, and find a hundred more twice as fun as the one before. You'll never use any of them short of a good game of Scrabble or the GRE verbal exam. Who cares!
Words are delicious and full of stories. Read about the them here in delectable detail and glory. Chew on each morsel of etymological insight...
Of course, it costs a fortune. And the CD Rom doesn't work on Macs. But those details can be overlooked if you have the money and shelfspace for the print editions.
By the way, if you buy the big OED... get a copy of one of the guides to help you through this thing. As enjoyable as the OED is, it is big and prepared by people who like abbreviating important things.
I fully recommend the OED.
Anthony Trendl