Abstract Graffiti (markers)
Just a little something I knocked up in a few minutes.

Next fill in the centre line and start the basic detail on the front, continue using the same box you started with, now is a good time to change any incorrect perspective lines.
Finish the basic detail and add the wheel arches.
Now fine tune the detail adding headlights grills and mirrors, I have also added indicator lights on the sides. You can now rub out the perspective box.
Now to tune it. You could skip this step if you want the car to look stock.
Now the wheels, this is the ugly phase, it is very easy to make the car look very high even if it isn't. Draw some lines to perspective that are where you want the wheels to be (my front wheel line is NOT to perspective because I want the wheel to look like it is turned.) Then draw the wheel as an oval onto that line, add another oval around (or inside) to make it look like a tyre. From the outer oval draw a line into the car to make the tyre look 3d.
Draw the rim inside the wheel (another tutorial coming soon to explain how to do this) and a brake disk. Then fill all of the areas that you want to be black with a black marker, also go over the lines with a thin ball point pen. I have added an interior but you don't have to. This step will show you if you got the tyres right.
Finish the colouring of the car, date and sign it and you are finished. I have added an orange outline to pull the drawing out of the page.
This final step was done on GIMP which is a free image editing program, I increased the contrast, darkened it, added headlights and a simple motion blur to the wheels.