Great examples of different styles of sketches from a bunch of reasonably famous projects - interesting to note the differing levels of detail and also the similarities to the actual final projects.
More and more after the jump...
5 Years of Firefox
iPad app sketch
Viget Labs Wireframes
Early Ember Sketches
OnlyJames Wireframe Sketch of Article Detail
Early BusinessWeek.com Design Sketch
Website UI Sketch
UI Flow Sketch
Dew Tour Wireframes
HBO SATC UI wireframe
Web Sketch Interface v2 – Graffletopia
Verify Home Screen