Excellent option - Magpul Industries AR15/M4 BEV Block

This unit performs well for most operations you need on an AR build, especially if you have a heavy duty adjustable vise to mount it in. The only thing I have found thus far that it fails at is in holding a barrel upside down to drill and pin a muzzle device to a 14.5" barrel. There are other inexpensive options to accomplish that though.