On the few I've dealt with, they just used a hanger bolt (a headless bolt with a coarse wood screw thread (lag bolt) on one end and a normal machine screw bolt's threads on the other), a big fender washer or a bar connecting both holes, and a nut. The bolt needs to go into blocking in the wall. If you used something like a lag bolt, the coarse threads would make snugging it up too dangerous. A little silicon caulk on the back will also act like a good glue.
www.wingits.com also makes some good wall anchors.