The officially recommended and supported by Apple USB Bluetooth Adapter is the
D-Link DBT-120, although as its quite old this can be hard to find nowadays (and pricey).
A list of other known compatible and not compatible USB adapters is here:
http://www.feisar.com/plugin_support.html#Bluetooth
I've heard positive reports about the *Edimax EB-DGC1* linked on the page above. It's £10.99 from Play.com and is Bluetooth v2.0 so will be faster for file transfers.
Also available from Play.com for £8.99 is the Sitecom CN-512 which I use on a Mac at work so can confirm that it works fine.
No drivers are needed for these on a Mac, so its just plug it in and go.
Julian
Aluminium 20" iMac 2.4Ghz, 2GB RAM Mac OS X (10.5.6)
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