Here's what I did (am doing) for my Garmin 260...
I got a cheap vent mount, then cut off the superfluous bits (so it's just a flat piece with the ball extension). I attached that to a proclip mount
http://www.proclipusa.com/moveclips/moveclips.aspx, which has no play and is very stable. The receptacle is attached (double back tape) in front of the CD slot (I use my iPod, so never use the CD player). The Garmin sits in the cradle it came with and attached to ball of the modified vent mount.
It is at the perfect spot, IMO. I can reach it without stretching or leaning forward at all and it's below the window level so it's rather inconspicuous. It can be removed, save for the bit taped to the dash (for now).
I am in the process of creating a clear receptacle out lexan and epoxy. I'm gonna try to make it so the CD player is useful. Will post pics when I'm done.
b
PS, I'm a big fan of Dremel.