Linux-friendly bluetooth dongle?

[Kendric Beachey]

This month's Linux Journal has an article about making your computer
auto-lock when you leave your desk, and auto-unlock when you return,
by sensing the leaving/returning of the bluetooth phone in your
pocket.  (You DO take your mobile phone with you....don't you??)  We
have a few jokesters around here that make this sound like a good
idea.

But neither my desktop nor my laptop have built-in bluetooth, at least
not anything Ubuntu 11.10 can find.  Does anyone know of a good
bluetooth dongle that works well with Linux?  (and is fairly
affordable?)

Kendric Beachey