La Rochefoucauld – Maxims
La Bruyere – Characters
Samuel Johnson – in his conversation
Lichtenberg
Emerson
Nietzsche
Oscar Wilde
Kierkegaard, e.g. in Either/Or
Mark Twain
Shaw

Come to think of it.. there aren’t so many books of aphorisms out there. So:

Books of aphorisms
Laozi – Tao Te Ching
Publilius Syrus – Sententiae (Moral Sayings) (~50BC)
Epictetus
Gracian – The Art of Worldly Wisdom
Nassim Nicholas Taleb – The Bed of Procrustes: Philosophical and Practical Aphorisms (2010)
Simon May
Pascal – Pensees
Wittgenstein – Tractatus
Ben Jonson – Timber, or Discoveries made upon men and matter, as they have flowed out of his daily readings, or had their reflux to his peculiar notion of the times
Halifax (George Savile, 1st Marquess of Halifax, 1633-95)

Halifax’s influence, both as orator and as writer, on the public opinion of his day was probably unrivalled. His intellectual powers, his high character, his urbanity, vivacity and satirical humour made a great impression on his contemporaries, and many of his witty sayings have been recorded. Maintaining throughout his career a detachment from party, he never acted permanently or continuously with either of the two great factions, and exasperated both in turn by deserting their cause at the moment when their hopes seemed on the point of realization. To them he appeared weak, inconstant, untrustworthy. But the principle which chiefly influenced his political action, that of compromise, differed essentially from those of both parties, and his attitude with regard to the Whigs or Tories was thus by necessity continually changing. Thus the regency scheme, which Halifax had supported while Charles still reigned, was opposed by him with perfect consistency at the revolution. He readily accepted for himself the character of a “trimmer,” desiring, he said, to keep the boat steady, while others attempted to weigh it down perilously on one side or the other; and he concluded his tract with these assertions: “that our climate is a Trimmer between that part of the world where men are roasted and the other where they are frozen; that our Church is a Trimmer between the frenzy of fanatic visions and the lethargic ignorance of Popish dreams; that our laws are Trimmers between the excesses of unbounded power and the extravagance of liberty not enough restrained; that true virtue hath ever been thought a Trimmer, and to have its dwelling in the middle between two extremes; that even God Almighty Himself is divided between His two great attributes, His Mercy and His Justice. In such company, our Trimmer is not ashamed of his name. . . .” [wiki]

Books that have been a source of aphorisms
Francis Bacon – Essays