Nice video on Paper Prototyping
I've always been a big fan of starting with paper.
Although it's hard to tell what the content is, it gives you a good sense of timing of a user interacting with a site. Amit Pitaru demonstrated and assigned paper prototyping when we had to design clocks for people with low-vision or blindness. This was mine my design.
This site shows sketches of very popular sites like Twitter.


