I've never met a Post-It I didn't like, but these are DA BOMB for keeping my studies organized! I originally started out with a sample pack of some narrow stickies, but I've settled on these yellow, one-inch wide, 200-count, repositionable Post-it tabs in a desk-gripping dispenser. I find I can write cleanly in pencil on them, erase as needed, and reposition several times, even though they retain a firm grip that allows me to use them to flip pages.
They also suit my OCD nature, as I can measure out their one-inch spacing easily with the ruler that I already keep handy to guide my underlining (see, really OCD). Look at my example below for how I notate for a couple of different classes. In one case I indicate an author and the title. In another class it's more useful for me to note the title and the lesson number reference. The difference is based on how I need to refer to materials for my midterm and final papers.
And that desk grip? Magical. If I didn't have the ability to slide it around my desk, I'd swear it was glued down!