Dictionary Definition:
a weak or imaginary opposition (as an argument or adversary) set up only to be easily confuted.
Also one of the early stages in the specification of Ada Language.
A candidate definition or statement presented to invite discussion, attack and modification. See Stake In The Ground.
Straw Man arguments are exceedingly common, big and small. A big Straw Man tactic, for example, would be the media's habit of pairing up two debaters, one of whom is certain of making weak arguments. Hannity and What's-his-name is a famous example, but more common is the big media practice of finding conservative Christians to argue this or that point--always with plenty of references to god and the bible. God, in any argument, instantly makes that argument a Straw Man, laughable to 95 percent of educated viewers. You WILL NOT find the media presenting conservatives with libertarian, nationalist, or isolationist leanings (with a few celebrity exceptions.) And if they do, you can be certain that the arguers are unattractive, batty, nonsensical, ineloquent, etc. The easiest way to win your battles is to pick your enemies carefully. As I said, this is not an argument, but a tactic, since you are getting Real Men who just happen to act like they're straw. Fred Phelps is the world's greatest living Straw Man, to the degree that he might also be an Agent Provocateur.
Some others:
(Surprisingly common). Pro-choice boosters claiming that pro-lifers "want" women to be raped and impregnated, or enslaved in the home, or killed by back-alley procedures.
Hints that a certain candidate "wants" a certain Iraqi dictator to be back in power. That is: If you are against my war which had effect X [which is the one good thing among 1000s of bad things], then you must be against X.
People who want to lower taxes must be against the poor, since the tax cuts disproportionately benefit the wealthy.
People against unions are against the working class. People who hate rap "music" hate black people. People who hate manipulations of the labor supply must hate job-seeking immigrants. Fits the pattern: "Practice X is associated with people Y. If you are against X, then you are against Y." Common, common, common.
Statements of the form, "The greatest president was Cal Coolidge", being refuted by, "Oh, right, so you're against the civil rights movement." The pattern is, "X was not associated with Y, thus if you are for X, then you are against Y."
"Why do you want to restrict access to firearms? Do you think I'm going to run mad in the street with an assault rifle?"
From Memes Shmemes: "A Straw Man has two features: it is easy to knock down, and it is a poor substitute for a real man." This sums it up nicely.
From Social Problems Of Lisp: "A Straw Man isn't the same as a weak argument. A Straw Man is when a weak argument is attributed to the opposition, and then (easily) refuted -- in order to make it appear that you've refuted the opponent's entire position."
For those who prefer pithy witticism: "A refutation of a caricature can be no more than a caricature of a refutation." -- Amos Tversky
Presenting an imaginary opposition in an argument is not always a bad idea, if this Anti Thesis is plausible enough. see www.fas.harvard.edu 
Someone should probably give a better example of a straw man than what goes on below.
Example Straw Man: Let's pretend that I think that the Federation from Star Trek is disrespectful to local cultures. I attempt to prove this by arguing that Captain Kirk is often disrespectful to local cultures. But this is a Straw Man; the example itself may be true, but it's a distraction from the larger issue, and doesn't (necessarily) map onto the entire Federation.
[This is not a good example - because Kirk is not set up in opposition to the point you are arguing. He is arguing FOR your position, not against it.]
A Better Example Straw Man: Arguing that the Federation is disrespectful it local cultures.... Captain Kirk says that we are ARE respectful to local cultures, citing the Federations required sensitivity training.
Well...this 3 hour course, which hasn't been updated in years, has been proven to have little effect on an officer's ability to interact with other cultures. Therefore, the Federation is disrespectful to local cultures. Captain Kirk (and his argument) are the straw-man, since they set us up to refute them, in an effort to prove a point. -- Mike Cole
so a Wicker Man must be a weak argument put forward to be burnt down in a huge ball of flames? Preferrably with your opponent inside.
See: Fallacious Arguments
See original on c2.com