My criteria were simple: (1) it shouldn't cost a lot, and (2) it shouldn't be too obtrusive. I asked our desktop support guys at work, and they pointed me to the Belkin #F8T016 USB adapter, which I ordered elsewhere for about $15.
It was remarkably easy to get working under Linux:
- Insert the USB adapter
- Boot the laptop using Linux
For the curious: this works exactly as you'd expect if you boot Linux first, then insert the adapter. Linux loads support for the adapter behind the scenes, and the Bluetooth icon appears on the desktop, like magic. You can remove the adapter at any time, if you are done using it.