Not really a tutorial, but certainly educational through the variety of techniques illustrated, this book showcases the sketching and illustration work of 24 design students from the Umea Institute of Design.
One more tutorial of note at Designertechniques.com is Hector Realubit’s hand sketching piece. Key points include his notes on shading and vignetting.
Another tutorial at Designertechniques.com focuses on traditional marker and pastel rendering.
Designertechniques.com has a lot of great info on car design techniques. One demo, by Ford designer Michael Smith, covers digital sketching in Sketchbook Pro.
A ton of video tutorials on sketching, marker rendering, and a few 3d topics are available on this page from MIT.edu.
Some interesting notes on observing and communicating form can be found at Saunders Creative. Click “resources>tutorials/lectures.”
If you’ve never spent any time at productdesignforums.com, you should check it out. Some time ago, user ScottieB posted a tutorial for sketching in AliasStudio. When I was getting started with digital sketching, info like this was scarce. It was written for a past version of the software, but the general ideas should be enough to get someone started.
Documentation for AliasStudio is sent with the software, but if you’re ever in need of it and find that it hasn’t been installed on your system, Autodesk makes it available on their site. In addition to the standard help info, some digging will produce additional goodies, such as pdfs that include a detailed introductory tutorial on technical surfacing, and information on data transfer between Alias and other packages.
Gnomon has introduced a new site called Gnomonology. It contains several short, affordably priced, downloadable video tutorials covering many aspects of 3d and animation. Software covered includes Photoshop, Maya, and 3DSMax. A few of the current videos might be of particular interest to designers looking to improve their 3d skills. Try “Intro to Subsurface Scattering” from Alex Alvarez and “Speed vs Quality in VRay” from Christopher Nichols.
Switching gears to 2D for a moment, Car Design News has a number of tutorials that focus on transportation design sketching and rendering. Inspiring stuff. And free! One of the instructors, Harald Belker, also has a few DVDs at The Gnomon Workshop.