Having used them for a couple of years now, I can confirm that Moonraker 4m mobile whips work very well. I have them on both of my vehicles, one with a Wouxun and one with an IC7100. They are easy to cut to length to get a 1:1 SWR.
The antenna has a PL259 fitting which attaches to a standard SO239 mount. An added bonus is the spring mount at the bottom, which prevents it from destroying itself if you drive into a multi-storey car park or hit an overhanging branch.
The Mirfield antenna which Selim mentions can be a useful quad-band compromise, but be aware that the SWR can be a bit high on the lower bands (they quote up to 2:1 on 4m and 2.5:1 on 6m) and in common with some other Chinese-made antennas, it may suffer in wet weather (of which we get a bit here in Wales!)