I wrote a two-part post on tumblr about drawing vehicles that I thought I'd share here as well, in case y'all might find it useful. I basically talk about how to gather up information and then use it to block out the subject in basic shapes, enough that you can then figure out the rest by using your refs.

Part 1
Part 2

The example images aren't super fancy (I didn't have time to do a whole step-by-step process), but hopefully it should come in some use.

Cheers!
-Tom