Slowhand's technique works quite well especially on post and burr rivets of the Copper, brass or steel variety. That's what I use mostly,
be careful the drill does not slip off . You can also grind away at the peened post with a small Dremal grind point ( careful of heat build up )
For the star style you will need to get at the little star teeth (I use a Dremel tool with a small round burr/file ) or if you have small side cutters
Radio Shack you can try to nip the teeth away.
For the Chicago style T style post & sleeve, the Drill with work, but in all cases where you use power go slow as heat will burn and discolor around the rivet.