This is the design I'm using currently.
I got a smoking deal on them through VistaPrint a year or so ago and I haven't gone through them all yet. I like to change up the look every now and then though, so my next order will be different.
One thing I feel is important is to use a car that you detailed if you put one on there. If you put a car that you obviously never have touched then people might question why you don't post your own work. I've always enjoyed going through pictures and picking out a good one for the card.