The Spring/Summer 2008 issue of Spectra Pulse Magazine features an article by Scott Lynch titled "Be Thou Familiar, But by No Means Vulgar: The Worst Cliches in Fantasy and Science Fiction." 

A brief look at a subject that could (and most likely has) filled entire doctoral theses, the article nonetheless contains a few worthy chestnuts:

And don't even get me started on Mysterious Mentors who possess the power to blast planets into atoms with a single fart, yet spend all their time wandering in the woods or being uselessly cryptic to the hero when they could just go deal with (Insert Dire Threat to All That is Bright and Wholesome Here) themselves and be back in time for a three-martini lunch. The desire to have it both ways with this sort of character, to withhold vital information or prevent obvious action for the transparent purpose of prolonging a flimsy plot, kills plausibility dead.

A quick, fun read, perfect while eating lunch at one's desk.