Augmented reality. It's that future tech we've all been waiting for--point your phone at something in the real world, and gain all the cyber knowledge the interwebs can provide. Wondering what species of tree you're looking at? Just direct your iPhone camera to it, and Wikipedia fills you in with a textual overlay.
Of course with the neat comes the not so neat too, so we at Mac|Life have done you the service of sifting out the junk. We've gone through just about every augmented reality app we could find, and here are our four favorites. They may not be the first apps you think of when you think about augmented reality, but they're actually useful. In fact, we'd say they're the best. And, iPhone 4 users, they're all updated for viewing on that gorgeous Retina Display.