|Ken Shirriff -> Java -> Fonts -> Learn|
Select the desired lesson and then click on the right answer. The "sense" button reverses the sense of which are questions and which are answers. When you get an answer correct, it is displayed above your score for review.
The source for Learn is here. A zip file with the necessary files to install Learn is here.
The kanji come from Jim Breen's kanjidic. This applet is inspired by jdrill.
I also have a PalmPilot version of Learn.
If you're looking for books to help you learn Kanji, I recommend Kanji Pict-O-Graphix : Over 1,000 Japanese Kanji and Kana Mnemonics by Michael Rowley. This remarkable book provides visual aids to memorization by tying the meaning of the characters to the radicals through drawings. I also find Essential Kanji : 2,000 Basic Japanese Characters Systematically Arranged for Learning and Reference by Patrick Geoffrey O'Neill to be a useful reference.