When using physical flash cards I use two distinct methods for determining which subset of cards to test myself on in a particular session and what happens when I get a card right or wrong. I'm implementing the same system online for Quisition.
The first is what I call short-term testing.
It applies only to the current pile being learnt (as opposed to older ones being reviewed) and I try to keep this to around 10 cards. I try to do this a couple of times a day and it usually only takes a few minutes.
I go through the pile testing myself on each one and putting them into a right pile or wrong pile. If there are no cards in the wrong pile, I'm done. However if there are, I go through the wrong pile again. If I get it right it goes in the right pile but if I get it wrong again it goes back in the wrong pile. I keep repeating this until the wrong pile is empty. Then I repeat the whole process again.
So there are, in effect, two while loops, the outer while loop testing (or retesting) all cards and the inner loop retesting the cards got wrong.
Note that the results of the short-term test don't need to be persisted. For this reason, I've implemented it entirely client-side in Javascript for Quisition.
I'll put up a demo short-term test in the next few weeks for people to try out. Subscribe to the announcement feed on the Quisition website to find out when it's available.
UPDATE (2006-01-21): Now see the demo.