Since it's VESA compliant, you can get any number of different bracket designs from arms through adjustable to static wall mounts. The VESA kits are normally in two pieces, one that you screw to the back of the unit you're mounting, and then whatever bracket/mechanism that you're putting up on the wall. You then screw or clip the two together.
We have our 32in LCD TV, which is probably slightly heavier than the iMac, up on a VESA mount. Just six bolts hold it in place in a breeze block partition wall, but it's not going anywhere.