The nook is great for out of print, out of copyright work you can't find. There's some great early sci-fi and pulp... And of course, Sherlock Holmes, Dickens, etc...
I picked up Dostoyevsky's complete works for less than $5.

Personally I found I did not like most of the completely free ones, because there was a sacrifice in readability.
But so many books of THAT length, and all those short stories, for so little? Well worth it.
