I’d have to say that there really is no “standard” format that is always used by everyone in the U.S. who writes a business letter. And of course, when using business stationery that already includes company name, address, etc., the writer’s return address is not necessary (but the date still is).

Some people line up everything along the left margin. Personally, I like to line up the date (and closing) so that they start in the center of the page.

As far as Bonnie’s comment about “always” using a colon after the salutation, there is an exception (— of course: it’s English!). It is acceptable to use a comma instead of a colon if the business letter is “informal” and if the writer and addressee are “friendly.”

For example –

Dear Mr. Smith: (formal and common in business writing)
or
Dear Ed, (informal and sometimes appropriate)

At least, that’s been my experience.

As well it is standard practice for business letters in the U.S. to be laid out using “full block” format. Using this format, the entire letter is left justified in the order that Cassie suggests. This is the only format I ever use for business writing.

The writer’s address and date should go on the right and the recipient’s address on the left, side-by-side (old style rules normally put the writer’s address higher on the page, and the date lower than the recipient’s address, to avoid having to type two columns on a manual typewriter – not a problem nowadays; the recipients address should of course be aligned to fit in the window if using windowed envelopes). I can’t imagine any circumstance in which it would appropriate to use a colon after the salutation…?