Arriva, the small Colorado outfit that makes those funky, wire-free headphones for the iPod Shuffle second and fourth generation, is now selling an intriguing--and sporty--set of in-ear Bluetooth stereo headphones that go by the name Leo.
These guys have that secure, comfortable fit that Arriva is known for (I used the Shuffle version of the headphones for running before my Shuffle died), and they work wirelessly with any Bluetooth-enabled MP3 player or phone.
They're water- and sweat-resistant and have controls built into the back of the headphones that are easy to operate by feel. There's also a microphone in the earpiece for making and receiving calls while you're doing whatever "extreme" sport you're doing--or just walking around (note: using the earpiece, you get mono, not stereo).

Battery life is rated at 5.2 hours (continuous listening time) and 20 days of standby time. Frankly, we think that's too short; we'd prefer something we can listen to all day.
The key thing the Leo ($69.95) has going for it is a secure fit. It's hard to find Bluetooth headphones that fit snuggly. Yes, the volume and power buttons are located directly behind your head while you're wearing it, but they're big enough to navigate by touch.