Is a great blog (put together by Jamaal Bradley) that collects and displays a range of animation pencil tests in all their glory. It's well worth a look if you're at all interested in animation... http://www.penciltestdepot.com/
What's an animation pencil test, you ask?
An animation pencil test is basically a video clip made from the animation drawings (called "frames") that, when shown at 25 frames per second on PAL TV systems, create the illusion of movement... BUT unlike the final piece of animation (as you'd see it in the cinema or on TV), the pencil test only shows the animation as simple line drawings (without the inking, colouring, and other effects that get added later in the production process to create the finished piece of animation).
A lot of people enjoy pencil tests because they often display a vitality that goes missing after it's been inked and coloured. In some cases the pencil test will also show the animator's thinking process, changes, and other notes, which provide a further insight into how the frame-by-frame animation was created.
To demonstrate what a pencil test is, here's a 5 second video from one of my old 1st Year animations dated circa April 2006.
(But obviously PencilTestDepot.com has animations of a much better quality! So go check it out).