The GoLink looks promising as well:
Products | goPoint Technology
It's a $100 OBD-to-iPhone cable. It gives you mileage/speed/RPM/etc data readouts, reads and resets trouble codes, charges the phone and does datalogging using an external website.
I think I'm going to order this, since I have an iPhone, and I've been wary of getting a SG since any gadget attracts thieves where I live. I had a digital tire pressure gauge stolen recently. Really.
