I have been using the Garmin Zumo 550 for my motorcycle for just over a year I believe.
This has been a flawless unit and has been in many downpours so it's very watertight, if that's something you care about.
The unit came with several mounts for use on several types of motorcycles as well as a car kit. I never even thought about putting it in the car then I got the Tacoma and gave it a shot. What I didn't realize is the car kit has an integrated hands free kit built in for using your phone.
The 550 has bluetooth connectivity so you pair it up with the phone and it will upload your recent history as well as your phone's phonebook.
When you get a call, you can answer or ignore and the speaker is quite loud. Those I have talked to using it say I'm very clear. The car kit has a suction cup mount and fits nicely just above the center of the dash.
This is not a cheap gps but, it also has XM connectivity and a built in mp3 player. The xm needs the expensive antenna to work so if you want to spend some extra $$ you can get it and have xm and xm traffic alerts. I use the mp3 - music stored on SD card - for the motorcycle. If you had an aux in for the stock head unit then you could plug in the output to that and get your mp3s through your speakers.
This thin is $600+ and if I didn't have it for the bike I probably would spend the money on something else... but, I really like this thing. There may be cheaper solutions with similar options but I needed something weatherproof and many of them just don't cut it there.
Anyway, I didn't see anything on the site about this so thought I'd add it. Let me know if you have any questions and I'll be glad to answer what I can.