Evernote
"Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at any time, from anywhere."
Use plain text, images, clippings from the web, or attach pdf's. Evernote lets you tag every note giving it context or categories. You can then search your information very easily via keywords or tags including the contents of your pdf's. Additionally, Evernote does some OCR on the server side, allowing you to also search the text in the hand written notes you scan in.