We made a iPhone application (or iPod Touch) that drills you on the proper use of Japanese particles in a format based on JLPT. Currently it has JLPT4 level stuff, but an update will introduce JLPT3 level stuff as well before the end of December. Of course, the update and additional content is free and automatic.
It's been getting a lot of downloads so far and people have been telling me they like it.