I have an i.Trek M5 which I got for about $70, and it works swimmingly well with Maemo Mapper. (I needed to pair it to my Mac to find the MAC address of the GPS in order to pair it by hand with Maemo Mapper -- automatic pairing didn't seem to work. I'm sure there's a way to browse nearby BT MAC addresses on the N770, but the Mac was handy.) The i.Trek M5 seems to be sensitive to being touched, though; if I touch it it gets a little jittery in the position it reports. (Not a big deal, though.)