Apple's recent iPhone 3.0 software introduction - as well as the new iPhone 3GS - finally introduces full A2DP Bluetooth audio support. This means not just the ability to stream to stereo headsets and wireless speaker systems via Bluetooh, but A2DP's much broader range of higher quality audio codecs much more suited to music listening than some of the lower bit-rate codecs used for voice calling. Unfortunately, iPhone 3.0 software doesn't provide support for Bluetooth's Audio/Video Remote Control Profile (AVRCP), which allows a Bluetooth accessory to control media playback. If you connect Bluetooth wireless headphones or to a speaker system that include playback buttons, only the Play/Pause button will work; you won't be able to skip or scan tracks or otherwise browse media content. This is just a software issue - and subsequent iPhone 3 updates may very well provide increased support for the full AVRCP protocol stack in a future update.

Here's a very affordable BT headset for under $35:

Kensington Bluetooth Stereo Headphones with Microphone

iPhone/Touch users may want to check out these articles:
Stereo Bluetooth & iPhone 3G with iPhone OS 3.0 at iLounge.com for more insights on OS 3's implementation of Bluetooth support.
MacWord's Dan Frakes' Bluetooth insights on paring, usage, glitches and gotchas you should be aware of.