Earbuds (or good ones, anyway) work like corks for your ears: sealing in music while blocking surrounding sounds. They're fine when you're safe at home, but not so much outside when you need to be aware of your environment.
While you might think it's crazy for a company to be selling one-sided headphones, there's a compelling idea behind them: If you're out jogging while listening to music you can always just take one of your regular earbuds out to keep an ear on your surroundings, but that only leaves you with half of a stereo mix in your other ear. So these One Good Earbuds simply mix your music down to a mono signal, letting you hear both sides of a stereo mix in one ear, and what's going on around you in the other.
They're available in three designs, including one with an over-the-ear support and the option for an inline remote control with a mic, topping out at just $27. At that price we're certainly not expecting audiophile grade sound here, but if it means you're not killed by that turning car you didn't hear, it's probably an agreeable tradeoff. [Far End Gear via Gear Diary]