Book I, 980a.21: Opening paragraph of Metaphysics
The first sentence is in the Oxford Dictionary of Scientific Quotations (2005), 21:10
Metaphysics
Variant: All men by nature desire knowledge.

“For legislators make the citizens good by forming habits in them, and this is the wish of every legislator, and those who do not effect it miss their mark, and it is in this that a good constitution differs from a bad one.”

Aristotle book Nicomachean Ethics

Book II, 1103b.4
Nicomachean Ethics

“The infinite… happens to subsist in a way contrary to what is asserted by others: for the infinite is not that beyond which there is nothing, but it is that of which there is always something beyond. …But that pertaining to which there is nothing beyond is perfect and whole. …that of which nothing is absent pertaining to the parts …the whole is that pertaining to which there is nothing beyond. But that pertaining to which something external is absent, that is not all …But nothing is perfect which has not an end; and the end is a bound. On this account… Parmenides spoke better than Melissus: for the latter says that the infinite is a whole; but the former, that the whole is finite, and equally balanced from the middle: for to conjoin the infinite with the universe and the whole, is not to connect line with line.”

Aristotle book Physics

Book III, Ch. IX, pp. 168-169.
Physics

“The proof that the state is a creation of nature and prior to the individual is that the individual, when isolated, is not self-sufficing; and therefore he is like a part in relation to the whole.”

Aristotle book Politics

Book I, Part II
Politics

“For pleasure is a state of soul, and to each man that which he is said to be a lover of is pleasant…. Now for most men their pleasures are in conflict with one another because these are not by nature pleasant, but the lovers of what is noble find pleasant the things that are by nature pleasant; and virtuous actions are such… Happiness then is the best, noblest, and most pleasant thing in the world, and these attributes are not severed as in the inscription at Delos: Most noble is that which is justest, and best is health; but pleasantest is it to win what we love.”

Aristotle book Nicomachean Ethics

Book I, 1099a.6
Nicomachean Ethics

“[S]ince causes are four in number, to know them all is the business of the natural philosopher, who also referring to the cause why a thing is to all of them, viz. to matter, form, that which moves, and for the sake of which a thing subsists, physically assigns a reason. Frequently, however, three of these causes pass into one: for the cause why a thing is, and that for the sake of which it is, are one. But that which motion first originates, is in species the same with these… [T]here are three treatises; once concerning that which is immoveable; another concerning that which is moved, indeed, but is incorruptible; and a third concerning corruptible natures. So the cause of why a thing is, is assigned by him who refers to matter, to essence, and to the first mover… But there are two principles which are naturally motive; of which, one is not physical, because it does not contain in itself the principle of motion. And if there is any thing which moves without being moved, it is of this kind; as is that which is perfectly immoveable, that which is the first of all things, together with essence and form: for it is the end, and that for the sake of which a thing subsists. So that since nature is for the sake of something, it is also necessary to know this cause.”

Aristotle book Physics

Book II, Ch. VII, pp. 124-126.
Physics

“Happiness, whether consisting in pleasure or virtue, or both, is more often found with those who are highly cultivated in their minds and in their character, and have only a moderate share of external goods, than among those who possess external goods to a useless extent but are deficient in higher qualities.”

Aristotle book Politics

Book VII, 1323b.1
Politics

“…suppose α without weight, but β possessing weight; and let α pass over space γδ, but β in the same time pass over a space γε,—for that which has weight will be carried through the larger space. If now the heavy body be divided in the proportion that space γε bears to γδ, … and if the whole is carried through the whole space γε, then it must be that a part in the same time would be carried through γδ…”

Aristotle

Book III Ch. II as quoted by Florian Cajori (1899), as Aristotle's explanation of why bodies fall quicker in exact proportion to their weight.
On the Heavens

“But the greatest thing by far is to have a command of metaphor. This alone cannot be imparted by another; it is the mark of genius, for to make good metaphors implies an eye for resemblances.”

Aristotle book Poetics

1459a.4
Poetics

“Remember that time slurs over everything, let all deeds fade, blurs all writings and kills all memories. Except are only those which dig into the hearts of men by love.”

Aristotle

"The Letter of Aristotle to Alexander on the Policy toward the Cities", translated from Lettre d’Aristote à Alexandre sur la politique envers les cités, an Arabic text translated and edited by Józef Bielawski and Marian Plezia (1970), p. 72; translated from an ancient Greek text that survived only in Arabic translation, there is little acceptance that this is an authentic letter of Aristotle.
Disputed

“[A]ll things as subsist from nature appear to contain in themselves a principle of motion and permanency; some according to place, others according to increase and diminuation; and others according to change in quality.”

Aristotle book Physics

Book II, Ch. I, p. 88.
Physics

“The law is reason unaffected by desire.”

Aristotle book Politics

Book III, 1287a.32
Politics
Variant: The Law is reason free from passion.

“It is well said, then, that it is by doing just acts that the just man is produced, and by doing temperate acts the temperate man; without doing these no one would have even a prospect of becoming good. But most people do not do these, but take refuge in theory and think they are being philosophers and will become good in this way, behaving somewhat like patients who listen attentively to their doctors, but do none of the things they are ordered to do.”

Aristotle book Nicomachean Ethics

Book II, 1105b.9
Nicomachean Ethics

“…. In a word, acts of any kind produce habits or characters of the same kind. Hence we ought to make sure that our acts are of a certain kind; for the resulting character varies as they vary. It makes no small difference, therefore, whether a man be trained in his youth up in this way or that, but a great difference, or rather all the difference.”

Aristotle book Nicomachean Ethics

Book II, 1103b
Nicomachean Ethics

“The best friend is he that, when he wishes a person's good, wishes it for that person's own sake.”

Aristotle book Nicomachean Ethics

Book IX, 1168b.1
Variants: My best friend is the man who in wishing me well wishes it for my sake.
The best friend is the man who in wishing me well wishes it for my sake.
Nicomachean Ethics