Can't get enough? Here are a few more great resources not mentioned, if you want dig deeper into Sketching user interfaces and interaction.

• "Why We Sketch," by Jared Spool. User Interface Engineering.
• "Sketch Sketch Sketch," by Joshua Brewer. 52 Weeks of UX
• "Forms, Fields and Flows," byDave Gray
• Brain Doodles, Visual Thinking Tutorials.
• "Think You Can't Draw? Here Are 6 Artists Whose Work Will Help!" by David Barnes.
• Konigi articles on Sketching.