For not much money you can get all sorts with lifetime maps, big screens etc etc. For bike specific I have only used the Garmin 660 (also does duty in the car) but it is pricey compared to how cheap the car ones are now. But it comes with car and bike cradles for charging and integrating in with comms systems. I use it in the car as a hands free device as well. It has its glitches with mapping and instructions, as do all GPSs.
I just checked a choice test on car ones, and the Navman EZY200 was the best performing cheapest ones, the best ones were TomTom VIA 260, TomTom VIA 280 and TomTom VIA 620 ($179, $199 and $249 respectively, all with the same score) For some reason the TomToms all had Borderline Victoria regional performance and the Navman poor NSW regional performance.