Only just noticed this post.
I'm no expert but I do enjoy photography and have been taking pictures of cars for years.
Some of the angles are interesting but some are just too much I think. I did like the low down shots with the car in the distance but the car needed to be more in focus I believe.
What camera are you using? Digital or 35mm?
I use a Minolta Dynax 5 SLR 35mm camera for my photos. I have stuck with this because I'm more of a traditional photographer and still prefer using the 35mm rolls although I do have a Sony digital camera for some shooting.
Have you tryed experimenting using a long exposure? or anything similar?
You know those photo's of cars at night when you can see the trails of all the lights? ~ This is really easy to do and give's some fantastic shots.
It's best to mount your camera on a tripod when doing time exposure shots and also to choose your location carefully so that you do atleast have some cars moving around otherwise it will just be static lights.
Definately start a portfolio though as it's a good way of observing your photography improvements and for experimenting