Ferengi Rules of Acquisition, as of DS9 Seasons 1 + 2
 
1: Once you have their money, you never give it back (Nagus)
2: You can't cheat an honest customer, but it never hurts to try.
3: Never spend more for an acquisition than you have to. (The Maquis Pt II)
4: Sex and profit are the two things that never last long enough.
5: If you can't break a contract, bend it.
6: Never let family interfere with profit. (Nagus)
Never let family stand in the way of opportunity (Nagus)
7: Always keep your ears open. (In the Hands of the Prophets)
8: Keep count of your change
9: Opportunity plus instinct equals profit. (The Storyteller)
Opportunity + instinct = profit.
Opportunity plus need equals profit
10: A dead customer can't buy as much as a live one.
or Never kill a customer unless the profit you make off his death is
larger than the profit you can make off his life.
11: Do business with a "Small Lobe" and your bound to get a big loss.
12: Anything worth selling is worth selling twice.
13: Anything worth doing is worth doing for money.
14: Anything stolen is pure profit.
15: Acting stupid is often smart.
16: A deal is a deal. (Melora)
17: A bargain usually isn't.
18: Beware of relatives bearing gifts.
19: Don't lie too soon after a promotion.
20: When the customer is sweating, turn up the heat.
21: Never place friendship above profit. (Rules of Acquisition)
22: A wise man can hear a profit in the wind. (Rules of Acquisition)
23: Never take the last coin, but be sure to get all the rest.
24: Never ask when you can take.
25: Fear makes a good business partner.
26: The vast majority of the rich in this galaxy did not inherit their
wealth; they stole it.
27: The most beautiful thing about a tree is what you can do with it
after you cut it down.
28: Morality is always defined by those in power.
29: When someone says "It's not the money", they're lying!
30: Talk is cheap; synthehol costs money.
31: Never insult a Ferengi's mother! (The Siege)
32: Be careful what you sell. It may do exactly what the customer
expects.
33: It never hurts to suck up to the boss. (Rules of Acquisition)
34. War is good for business. [Quark, "Destiny"]
35. Peace is good for business. [Dax, "Destiny"]
36: Too many Ferengi can't laugh at themselves anymore.
41: Money talks, but having lots of it gets more attention.
42: Be loyal to your allies occasionally, so they will forgive you when
you cheat on them.
43: Caressing an ear is often more forceful than pointing a weapon.
47: Don't trust anyone wearing a better suit than your own. (Rivals)
48: The bigger the smile, the sharper the knife. (Rules of Acquisition)
57: Good customers are as rare as latinum--treasure them. (Armageddon Game)
58: Friendship is seldom cheap.
59: Free advice is seldom cheap. (Rules of Acquisition)
60: Never use credit where your words will do.
61: Never buy what can be stolen.
62: The riskier the road, the greater the profit. (Rules of Acquisition)
70: Get the money first, then let the buyers worry about collecting
the merchandise.
75. Home is where the heart is, but the stars are made of latinum.
[Quark, "Civil Defense"]
76: Every once in a while, declare peace; it confuses the hell out of
your enemy. (The Homecoming)
79: Fighting with Klingons is like gambling with Cardassions; it's best
to have a friend with a weapon around when you lose.
101: Never do something you can make someone do for you.
102: Nature decays; but Latinum lasts forever. (The Dominion PartI)
103: Sleep can interfere with ....(opportunity, profit, ?????) (Ferengi
cut-off in mid- sentence) (Rules of Acquisition)
109: Dignity and an empty sack are still worth an empty sack. (Rivals)
or Dignity and an empty sack is worth the sack
111. Treat people in your debt like family; exploit them. - Past Tense,
Part I
112: Never have sex with the boss's sister. (Playing God)
119: Buy, sell, or get out of the way!
123: A friend is only a friend until you sell him something; then he's
a customer.
139: Wives serve, brothers inherit. (Necessary Evil)
172: If you can sell it, don't hesitate to steal it.
194: Always know your customers before they come through your doors.
(Whispers)
214: Never begin a business negotiation on an empty stomach. (The
Maquis Part I)
217. You can't free a fish from water. [Quark, "Past Tense, Part I"]
284: Rules are always subject to interpretation.
285: No good deed ever goes unpunished. (Collaborator)
286. When Morn leaves, it's all over. {Quark, "The House of Quark"]
This was a joke, since there are only 285 rules

???: Never have sex with the boss's daughter. (Playing God)
???: You can always buy back a lost reputation.
???: When the Grand Nagus gives you an opportunity, leave town until
he's gone!