I bought a Garmin Nuvi 200 a few weeks ago. It's small enough that it fits nice with 2 small bungies over the top plate (where it reads Hayabusa) and the raised chrome bolt caps keep it from moving left and right. A stem mount or tank mount are other options. I have a tank mount I use for my camera, but I find the GPS easier to see up by the gauges.
I used it on a road trip two weeks ago and it was incredible. I found kickass roads that I never knew existed. I rode about 50 miles out into twisty, heavily wooded hills getting myself thoroughly lost. Turned it on, clicked on my hotel and it got me back in no time.
It's a standard size touch screen but it's very thin compared to most other models. It'll fit in your shirt pocket. Internal batteries will keep it powered well over 5 hours and it can be recharged with the car adapter or through a USB port. Recalculations and detours are instant. On max volume I can hear the voice prompts up to 40 mph with my helmet on. Screen never gets washed out from sunlight and it always has a good signal even inside my house. If you want to take a scenic route home you can tell it to avoid highways or toll roads.
For finding any address, it's dead on accurate and will get you right in their driveway.
I haven't tried it yet but there's some kind of option that warns you of speed cameras. I think you download from a collective database and it'll tell you when you are in a danger zone.
My only complaints are that it does not have a headphone jack and even though it has the 2008 road maps, some newer highway modifications made within the last 6 months are not on it. I80 to 394 ramp in IL is one and 6 Points in Indianapolis is another.
Since there are so many units to choose from you need to search for reviews. Beware of some models that have extra gimicks like MP3 and video players...many suck when it comes to being an actual GPS.
cnet review Nuvi
It's come down in price from the $400. I paid $250 at Circuit City. Plus another $100 off thanks to my Speedy Rewards gas station points.