OK, I'm an admitted and easily recognizable gadget freak. But I think this will have broader interest to folks who are active runners or who work out frequently.
I'm a long-time Cingular 8125 user (best phone, best PDA I've ever had) and I always take it with me on my runs and listen to music or audiobooks while running. I've gone through countless headphone configurations, but I've used the Motorola HT820 bluetooth wireless stereo headphones for a couple of years and absolutely loved them. My only complaints were they were too large (the kids said I looked like Mickey Mouse running with them on), the controls lacked adequate tactile feedback, and they just couldn't take the sweating attendant with running in Mississippi. In fact, I've gone through three sets of the HT820s (not cheap).
If you're a runner or exerciser who listens to an MP3 player while you work out, I'd highly recommend the S9s.