I stumbled across this site while doing research the other day and must have wasted 20 minutes tooling around on it. It is a new flash application called Turning The Pages – part of the British Library online. With it you can do a virtual flip through literary classics and other famous manuscripts – all in the hand of the original author. Since it’s new there aren’t a lot of choices yet, but it’s worth bookmarking and revisiting as they continue to add to the volume.
I’ve always idolized Da Vinci, so I recommend you start with a look at his sketches.