comma - Everything2.com

A concise summary of comma rules:
(the safest rule: Don't use a comma unless you have a reason.)

Use commas between items in a list...

using words: "Please pick up some rice, soy, and ginger at the store"
using phrases: "You can open cans, slice carrots, and bake bread with this magical appliance!."
using clauses: "I can't decide which classes to take, how I'm going to pay for it, or where I'm going to go."

Use commas in coordinate situations

Compound sentences with a conjunction: "I'd send you the money, but my bank messed up my last deposit." (see also)
Compound sentences after a semicolon and a conjunctive adjective: "The storm pounded; however, no damage was done."
Adjectives (but only if their positions can be changed without altering meaning): "It's a fast, cheap, robust solution to your problems."

Use commas after introductory elements in sentences

Nouns of address: "Dave, I'm sorry I can't do that."
Mild Interjections: "Well, I'm sorry I'm not going to be able to make it tonight."
Groups of prepositional phrases: "In the house without anything to do, he stayed up all night noding."
Participial words and phrases: "Regarding our research, please note our wonderful discovery."
Infinitive phrases: "To set the server up, just follow the instructions on page 802."
Subordinate clauses: "Soon after he saved his term paper, the power went out in the lab."
Absolutes: "The matter already decided, he concluded to go about his business."
Transition words and phrases: "First of all, I should explain my position."

Use commas to set off interrupting elements

Nouns of address: "I'm very sorry, Mrs. Davies, but your hard drive can't be recovered."
Appositives: "He bought a new car, a 1990 Honda Civic."
Contrasting elements: "The software, not the hardware, is the problem in this case."
Unnecessary descriptive phrases: "Iced tea, with or without lemon, goes great with chicken fried steak"
Unnecessary descriptive clauses: "The core dump, which can sometimes be useful, won't be any help to us here."
Absolutes: "Mark jumped at the sound of his alarm, its music blaring."
Parenthetical expressions: "We will ship everything at once (e.g., hardware, software, documentation)".

Use commas in standard places

Between parts of addresses in a sentence (but not zip codes): "1401 W. Airport Frwy., Euless, TX 76040"
Between and after parts of a date: "Sunday, October 8, 2001"
To set off direct quotations: "Thomas said, 'That's not true'."
In a business letter after the close: "Sincerely,"
In a personal letter after the opening and close: "Dear Frank, ....... Thanks,"
Between and after titles: "Mark Smith, Jr., is the only son of Mark Smith, Ph.D."
When reversing first and last names in a list: "Smith, Mark"
To change a statement to a question: "You're the boss here, right?"
In numbers: "123,456,789.00"

Source: Personal notes from High School English class.

serial comma	comma before conjunction	punctuation marks	Where to go for help with punctuation
Harvard Comma	;	Billy Cranston	If you really mean it, set yourself on fire
colon	code to comma-delimit numbers	Japanese writing system	semicolon
period	Eats, Shoots and Leaves	peripheral neuropathy	rules of typography
Sméagol	Is the fact of your certain death enough to prevent you from enjoying life?	Paint it Black	coma
Hunting for commas	Cereal box marketing	Editor Log: June 2005	Turbo vs. supercharger