Evernote

Click here to Buy it Now from Apple App Store, Free

If you own a smartphone, you should already have Evernote. The ultimate productivity app (we use it for damn near everything), Evernote lets you take and save notes, take and save photos, make to-do lists. The uses double when you use Evernote in conjunction with other apps. Just download it, you'll figure out your own ways to use it.