I have had the Garmin StreetPilot 2610 with a 512MB CF card for several months. It is a great unit and I highly recommend it due to the remote control and the screen clarity in all lighting situations. (ie. Bright sun, night time, etc.) Plus, they were on sale at Amazon.com for $529 just the other day. $729 w/ two $100 rebates.
I also bought an external antenna when I realized the unit would not fit on the Viper's small dash. I purchased the Gilsson antenna with the 3 ft MX cable for $26 with shipping.
I put the GPS on my center console with the bean bag mount and the Gilsson on dash. If you get into some spirited driving, you will have to place the 2610 on the passenger seat or on the floor to give you room for shifting.
I looked at GPS units for a couple of months before buying my first one a few years ago and the Garmin was the unit of choice on most forums. The Streetpilot is a excellent model for car navigation and I know you will be pleased with it.