I just installed this Bluetooth ELM327 obd2 code reader and had a quick play around with the Torque (Lite) app for Android and I have to say for just US$7.99 including postage I am happy with it.
Read all the diagnostic data I attempted successfully and the refresh rate makes it very responsive.
Plug and play in under 60 seconds.
I got the v1.5 Bluetooth ELM327 Mini adapter unit and it fits without impeding access to the compartment in front of the port.
I did have to unclip the OBD2 connector from the stock mounting point so I could close the compartment, which was very easy even with my fat fingers.
Not sure about whether or not it will rattle around when driving but that can no doubt be easily resolved with a cable tie or some other way of fastening.
Removing the device from the OBD2 connector will invariably pull the connector forwards and clip it back in to the original mount, so no worries there.
All in all pretty sweet and discreet little unit!
I am sure there are better products out there and I don't know how reliable or robust it is yet as I literally just installed it, but I'm happy with it so far :-)
I'll update this thread if anything else worth sharing comes up.
Let me know if I can answer any questions!