OmniFocus is a productivity app that helps you get things done (it works with the GTD methodology, too). It's certainly not the only task manager available for the iPad, but what sets it apart is its understanding of contexts. For instance, it will remind you about all of the food you need to pick up when you're at the grocery store, but you won't see that stuff when you're at the hardware store. It can sync with OmniFocus for Mac, iPhone, or iPod Touch via MobileMe, WebDAV, Bonjour, or the creators' own Omni Sync Server. The app is not cheap and it takes some time to learn, but if you already use it on your other devices, it's worth the cost.