I am using a Navigon 8410 which with very simple hacking will run SD perfectly.
Its advantages are:
- Sunlight readable
- 5" screen .. large enough in my view, esp if you use Tim's device.xml file to control DPI.
- V lightweight and portable
- Charges via USB cigarette lighter
- Lots of cradle/holders for very easy "snap in" fixing
- Good GPS fix (8 sats usually once initial 1/2hr fix is done)
- Available for circa £250
- V good car navigation as well
Cheers
D