How many buttons

The amount of buttons a single-breasted suit jacket should sport is really a matter of personal preference, but let me offer the following.
One Button
A single button falls into the realm of a fashion suit; it's been a trend before and will go out again. And there's a reason for it: within reason, the more buttons a suit jacket has the taller a gentleman looks (yet another of the visual tricks a suit can perform). So it stands to reason that a single-buttoned suit does the opposite to conveying stature. So unless you're over 6' 2", I'd suggest you avoid a single-buttoned suit.
Two Buttons
My preference for a modern suit. It conveys height, slims the waist, and fits perfectly within the realm of fashion and classicism.
Three Buttons
Very much a look of the 1990's, it's making a come back and has been seen amongst the tailored wares of Tom Ford and Ralph Lauren's Purple Label. Three buttons convey a greater sense of height than a two button suit, but are harder to pull off. I own several, and wear most of them in a fashion-forward sense. Definitely one for the more confident amongst us.
Four Buttons or more
Please don't. I'm yet to see any four button suits offered in 2009 which truly impress me, fall within current men's trends, and will figure in as a good investment piece beyond this year.