There are various designs for angle-grinder stands:

fixed stands

• no mount needed, just camp it in a vice? another guy does it and another guy!
• support/stop for when grinding (nifty)
  THIS. This is the one I want to build. It's not immediately obvious, but the cross-bar piece clamps into the vice as well, which means the cross-bar-piece is stabilized at two points. This makes it much more secure than you might think at first.
  
  
• adjustable on two axes
• strong
• adjustable on two axes (commercial product)
• adjustable on one axis; rather simple
• with a flat table section, like that's used for sanding
• with a flat table section another post from the same guy
• flat table + zip ties
• U-bolt

chop saw stand

• one of the commercial ones