If you're feeling a little guilty over that new iPad preorder, you could try convincing yourself you'll use it for something positive. The Khan Academy may be of assistance there, as it's just released an iPad app that makes over 2,700 educational videos available for free. The videos are all in Salman Khan's trademark low-tech style, involving Wacom tablet doodles and simple, conversational explanations to help you get to grips with a whole range of topics from computer science to the history of art. The app is pretty straightforward, but offers useful features like subtitles, progress tracking, and the ability to download videos and playlists for offline viewing. It's free and available in the App Store right now.