I found a couple of pretty good Garmin voices on the torrent sites for my GPS, one of Arnold and one of Stewie Griffin. The both sound like they were captured from Arnold's movies and Family Guy and pieced together without Arnold or Seth McFarland doing the recording session.
I also found a site selling voices of sound-alike impostors doing Dr. Emmet Brown, Kit, and Yoda. (Doc Brown sounded great.)
I guess the next logical step is for someone to assemble one of Majel Barrett's computer voice from TNG, DS9, and VOY. Or is there one already?
Computer voice would be cool... I'd buy it.