I use a mapping system call Street Atlas USA along with an Earthmate GPS on my notebook.

I pick my rental car, open up my computer on the passenger seat, attach my GPS via usb and within 2 minutes, I'm good to go.

I've got all of my customers locations "marked" on my map file. Makes planning a trip a piece of cake.

While driving the little green arrow shows direction and also speed. It even helped get me out of a speeding ticket outside of LA.

Best $150 we ever spent!!