Ah, sorry, didn't mean to desert my topic like that.
That being said, I wasn't really looking for suggestions on how to outfit my merc -- I was just curious as to what everyone else was doing. In answer to your question, though, I'm running a hammerdin with an act 2 merc (mostly out of habit, I suppose). At the moment, he's using:
Sigon's gauntlets
Sigon's belt
Sigon's helm
Sleepthorn (unique spear with 80% slow)
Knell of Discord (ring with knockback & lifesteal)
Nameless Fear (ring with increased attack speed and prevent monster heal)
Shattering Blow (breastplate with crushing blow 1% per character level)
He's pretty badly in need of an upgrade I guess, since he's above level 70, but he's surprisingly efficient. I'd like to get a holy freeze aura on him, but I don't want to lose any of the other capabilities he has. The only place I could really see trading out an item would be his helm, and I don't know of any holy freeze helms out there.