The Zumo 550 GPS is the high dollar way to go, great GPS with built in XM and cell phone interface, water resistant and has motorcycle mounting options, it was designed for motorcycles, but it isn't cheap 650 to 850 depending on where you buy it.
I went with Sirius, my rig is cleanly mounted on a RAM mount and I made the adapter to mount it to the round RAM mount. The chrome bar sticking up is a locking mount - (work in progress). It will have an aluminum block milled and attached to the top of it to secure the unit in place and it will be cut down to extend about 3/4" above the unit.
The buttons (presets) are small. I have an old helicopter headset plug with about 6" of cable left on it hanging from the mount, I use it as a stylus and it hangs neatly between the switch housing and RAM mount - otherwise I couldn't tune it with gloves on.
Downside, my rig is not water resistantso I cover it with a leather bag in the rain. Upside is it cost 100 bucks and I can pop it off and mount it on my home mount in my garage, or on my other car mount in my car.
The 12 volt adapter is hooked up inside the left fairing under the left fairing cargo compartment. Initially I had an irritating whine in the audio. Had to install a ground isolator from Radio Shack, then it worked perfectly.
Ground Loop Isolator
Model: 270-054| Catalog #: 270-054 $16.99
See topic: https://www.goldwingfacts.com/forums/forum1/80244.html
I bought the short wired antenna from these guys, they also have some motorcycle mounts: http://www.tss-radio.com/