A flash card is usually an index card with question on one side and answer on the other side. You can then shuffle you card and test yourself. Flash card is very efficient for studying. In college I had to make flash cards and it work really well. The downsides are that the piles of card actually grow too big to handle, it's time consuming to make, and you need to run out and buy more index cards to make flash card.
Being an electronic hobbyist, I want to make sure I get a proper education without have to pay for college. (Remember EEVblog #92 - Get your MIT Engineering Degree for FREE?) I purchased college textbooks on ebay, but I still need a way to test myself. This is what I use. But I want to be more advance, I don't want to lose most of what I've learn. I believe this will be useful for some people in here working on some sort of exams.
That reminds me, I need to make a flash card on basic rules of boolean algebra.
A+0=A
A+1=1
A*0=0
...
It's a good way to keep my mind sharp
I know there are many flashcard websites online. Most of them require you to register and that you make your flash card online. That is slow and bothersome for me. Here, you make your flashcard using notepad. When you are done, send it in and play with it. You'll keep the original, the site will keep your copy. Whenever you update your card, just send it in again. To share your cards with a friend, tell your friend the filename of your card. He or she can either type in the 2nd box and the file will be retrieved. The website has been design so that even an arabic, chinese or japanese user can use it too.