Frustrated with the fit of your MP3 player's stereo earbuds? I don't blame you. Some are notorious for popping out at the slightest provocation—particularly those made of hard plastic that don't come with foam covers. Others, including Apple's ubiquitous iPod earbuds, do come with the covers, but the foam tears easily and the pads are often lost. Still others—namely Creative's Zen Aurvana earbuds—fit securely but transmit tremendous, booming sounds into your ears with each slight pull of the wire (read: with every step you take while walking or jogging.) Enter the Sennheiser MX75 Sport earbuds, which are designed specifically for the fitness enthusiast.