You've probably seen Matthias Lange's Bluetooth Clipset and FlipCams, but his new MP3 Pocket Player, is his first design I know I'd buy. It was designed to be comfortably used while worn in your pants pocket. Apparently the device's curved shape allows all relevant controls and the display to be visible, whether it's stuffed in your pocket or in your hand.
For the most part I only listen to my MP3 player when I'm working out (in which case I wear an arm band) or at my desk (which means it's resting on my desk). My boyfriend however, is one of those awful pocket offenders, who seems to cram as many gadgets and items in his pockets as possible. Wallet, Chapstick, keys, Video iPod...you name it. I love the idea of an MP3 player that was created with his type in mind. The actual player is a tad masculine for my taste, but clearly men seem to be more into stuffing their pockets than women.