I've been wondering when flashcards would meet the iPhone. I now wonder no longer.
The two have met at long last, thanks to iFlipr. It's a free flashcard site that, while specifically designed for the iPhone, will work on a regular computer, and even most older phones with internet access. Like many of the better flashcard programs and sites I've discussed, it employs the Leitner System, so that you're quizzed more frequently on items with which you have more trouble.
Rather than a long description of the features, check out their introductory video:
I like that it can be used on my desktop, but for portability I may just have to pick up an iPhone after all. Although, I'm probably not going to even get near an Apple Store tomorrow.