I hate being one of those guys that drags up old threads and posts, but I wanted to chime in on this, as basic drawing skills are CRUCIAL for what I do illustration-wise. It's what's holding me back currently from working on my first big/new airbrush (assisted) illustration. I've got my research materials together, the concept(s) - but I need to get my hand in order before I can really get started.
I grew up being "the kid who could draw" - and we used the Betty Edwards book in high school art. I highly recommend it, especially for beginners. If you feel like you need to push a little further, I have a few other suggestions:
Sketching: Drawing Techniques for Product Designers
Sketching (12th printing): Drawing Techniques for Product Designers: Koos Eissen,Roselien Steur: 9789063691714: Amazon.com: Books
--excellent book but pretty advanced. has a nice section on perspective drawing, which is something I was never taught in school (but should have been) - big tip from this book: before you start drawing, WARM UP. I do this as often as I can and it really helps if I'm always drawing boxes or other shapes in perspective, circles or whatever else comes to mind. It also covers light/material/reflection/stylization, etc...very good stuff.
Sketching: The Basics
Sketching: The Basics (2nd printing): Roselien Steur,Koos Eissen: 9789063692537: Amazon.com: Books
same authors, more basics though. I haven't read this one yet but it's on my list. You're never too advanced to get back to basics.
I'm about to start this book:
Successful Drawing (by Andrew Loomis)
Successful Drawing: Andrew Loomis: 9780857687616: Amazon.com: Books
It's all about light and perspective. I encourage everyone to buy this of course, but it has only just recently been reissued by the publishers. Before that, someone found a handful of Loomis' books, scanned them and put them on the internet. These books are considered an incredible resource due to their depth, ease of reading/understanding and so on. I've downloaded this and several other of his books for previewing, but I will wind up getting hard copies just because they are valuable resources.
I also like:
Industrial Design Sketching and Drawing Video Tutorials
Core77 / industrial design magazine + resource / home (decent discussion forum for all sorts of product design)
Coroflot (lots of on-line portfolios from every sort of professional artist that you can imagine - tons of forward thinking design, illustration and artwork.
Dwayne Vance, Chief Creative Officer at Masters of Chicken Scratch from Corona, CA --cool illustration and he designs Hot Wheels)