Try http://www.cycoactive.com/gps/gps_mounts.html. I got one for my Garmin 2610. It's lockable, so you don't have to lock it in your trunk if you're eating lunch or whatever during the day. I still take it out at night when I'm on the road.
The mount is sort of ugly, but very functional!
Oops! Forgot to tell you...it's the Touratech mount.
What I always recommend is to sit on the bike in riding attire and position and have someone place the GPS in the positions you're proposing to mount it at. If you don't have the GPS, you can use a business card since most of the Garmin units have a display roughly close to that size.
With your helmet on (if you ride with a helmet), try diverting your eyes from the road to your mounting positions and try to focus enough to pick up the detail on the card for 1-2 seconds.
Everybody's eyes are different and some people need to have the unit mounted in one focal distance over another. The other thing to be aware of is how far you have to divert your eyes from the road to read the unit (and you WILL be looking at the unit occasionally, no matter how much you think you're going to rely on the audio output).
I vote for the Ek mount. Sturdiest mount I have ever used or seen. Its sit down in the handlebars a little bit, not sticking out and up like a sore thumb. I believe it also helps with the visibilty of it in regards to people walking by and seeing it. I just barely have to look down to see it. Works perfect and he is a great business man to deal with.