Guerilla Marketing - J Conrad-Levinson
Made to Stick - Chip & Dan Heath
Ogilvy on Advertising is brilliant as well, by David Ogilvy obviously!
Seth Godin's wrote some good stuff as well. The Big Moo, Meatball Sundae, etc.
Oh, nearly forgot. Probably my favourite and likely many people's favourite, Influence - Robert Cialdini (not really a marketing book, but a must have book for those in marketing).