I'm a big fan of Bluetooth GPS units. With these, I can have my GPS based location (and routing) no matter where I am, without making my device bulkier than I'd care for. One of the available Bluetooth GPS units is created by Teletype, and Freepaq has put up a review of that product. They're pretty pleased with it as well:
"This Teletype GPS thus holds all its promises with an astonishing sensitivity and a perfect design (except for the button). The sensitivity is definitely higher than the Navigon GPS for example and is higher than the EMTAC, this last being for me a reference point. Very good GPS." 
Freepaq Reviews Teletype Bluetooth GPS
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