Jarnal is a plattform-indepenent programm written in Java for notetaking, sketching and PDF-/picture-annotating. It works like a normal notepad with the difference of being digital. It is thought to be used with a stylus on tablet-pcs.
Works extremely well with Bamboo tablets -- digitization of pen strokes beats all other $$$ programs I've tried, including Microsoft One Note and Adobe Acrobat pro.
I am hoping for an android port for this application or Xournal.