More or less recently I paged through several of those books full of isolated quotes. I feel the intrinsic value of these to the serious bookworm is something less than nothing.
Instead of these I would rather recommend certain book in the classical canon, which provide one with an extensive repertoire of quotes; and some you may find for yourself, that are more applicable, suitable, and usable.
Homer, firstly, in a good translation— Pope’s is classical, and therefore eminently quotable— but any good, straightforward translation will serve.
A good bit of Tennyson, also. I read through a copy, a bit here and a bit there— that might work for you, it might not, it depends.
Shakespeare, of course, is quite indispensable. Hamlet, naturally, and Macbeth, and the ones about the English kings—but beware, he insults St. Joan of Arc. (I’m still mad about that.)
Shelley (an atheist), and Byron, I suppose, are next on the list. I’m ashamed to admit, I’ve never read any Byron, but I’m sure he’s often quoted.
While there is a great deal that I’ve missed, I hope this will inspire you to read some good, classical books. Enjoy!