My friend Kevin Kelly, a co-founding editor of Wired and author of several excellent books, including Out of Control and Asia Grace, is a documentary movie junkie. True Films, his 56-page PDF book, reviews 100 of his favorite documentaries.
"True Films" contains the best 100 documentaries I've reviewed on True Films as of December, 2004. I winnowed some from the larger list, and came up with an alphabetical collection of 100 documentaries I feel are worth your time. Most people will enjoy the majority included. There's been one private film club launched around this list.
What you get for your $3: a downloadable PDF file of a color version of the book (which was printed in B&W).