I think Evernote is pretty decent for this. I just use the web version, but because of the work I do, I have to read a ton of documents online and usually want to refer to them later. Evernote helps because I can use the web clipper to save whatever I am looking at and then tag it and even write some notes on it. Then later I can fire up the desktop application and go through my notes.
I believe the mobile versions allow for hand writing but I've never used them.