Sure you could use your level app on your iPhone to hang a frame on your wall, but for larger jobs check out Black & Decker SureGrip Laser Level ($30). Not only does the SureGrip utilize laser to cast a level line, this handy tool also comes with a rubber suction cup wall mount attachment that sticks to a variety of surfaces for up to 2 hours without leaving a mark, so you can work freely with both hands.