Handwritten notes are great (as long as they're complete!), but if you want something a little more searchable, re-usable, and less easily lost, here are some options. If these don't meet your needs, come talk to a librarian, or just use handwritten notes.
Whatever you do, make sure you keep GOOD notes. There's nothing more frustrating than writing up your paper and realizing you missed the volume number on a journal citation or the publish information on a book citation and having to backtrack. We've all done it, and it's not fun!
Questions? Contact firstname.lastname@example.org