I've been using a Larsen NMO antenna for the past several years. There may be something better out there but I haven't found it. Take a look at page 100 of the Ham Radio catalog
http://www.hamradio.com/web/newcat/hrocat9.pdf
You will need the antenna and a mount. I have the trunk lip mount on one car and the mag mount on the SUV. Both have served me well for four or five years.
I like the fact they are not overly tall, being NMO they can be unscrewed and a cap placed on the mount if you don't want to have the antenna seen. Of course you lose reception that way. I take them off when I have to leave the car at the airport or something like that.
I recall paying something like $30 for the mount and around $40 for the antenna.
I can even pick up the low powered McDumbDumbs most common drive through VHF-LO freq up to half mile away.
For VSP, I live in the Yorktown area and I hear some of the Richmond freqs routinely in the car. I have picked up the VSP low powered TAC channels two or three miles away (maybe further, but I wasn't really checking). For the York/JCC system, I lose it south of the HRBT.
Before I got the Larsens. I used the RS tri band scanner antenna. About twice the height and I think poorer reception.