if you want a nice touch screen gps that gives u accurate speed. I would use any of the garmin range.
the one i have is a c510 and its excellent, when i had the 4wd with big tyres the speedo was out 30k/hr when traviling high speeds, it was good and i would say its very accurate as i never had a speeding fine and have done over 100,000ks in the beast!
if u want a fancy model than the c510 look at the nuvi 660 - has blue tooth and mp3 player etc, flat wide screen!
heres a link for u
http://www.gme.net.au/garmin/mobile.php