Anyone who’s into product design should certainly check out the Product Design Forums site if you haven’t already. It is a big discussion forum full of Industrial Design professionals, students, and fans. TONS of excellent tutorials, as well as exercises and competitions. For instance, every month there is a sketching exercise thread, where everyone sketches and scans based on a given theme. I haven’t participated very much yet, but I really want to start because I know that the practice and feedback will do nothing but help me.
It’s not all sketching either. There are tons of great resources and references for Solidworks, Photoshop, and other software packages in the 3D Tutorials category.