I brought a plastic self adhesive plate from Halfords (75p) that's designed to provide a good airtight surface for satnav. This I've stuck to the plastic trim beneath the dashboard above the transmission tunnel. Using the suction cup mount on my TomTom this allows the display to be located neatly over the tunnel in front of the radio. You need to set if reasonably far back to stop touching the screen when changing gear (1st, 3rd and 5th).
Its low down, unobtrusive and down there it's generally shaded from the light, most of the time I just listen to the voice commands with a quick glance if necessary. Its location however is very close to the power socket, so you can buy a short power lead to eliminate wires in the foot well.
