Sneaky bastardism. Use terrain, use hazards, and start thinking of frontal assaults as a pathology, not a tactic.
Not sure if you've seen this article, but its something I've used as a blueprint the few times I've dmed.
http://www.tuckerskobolds.com/
Heh. I did things the players still speak about in whispers to a party with nothing but kobolds.
Bloody idiots didn't set a night watch... After all, level 20's don't NEED any stinkin' night guards, right?
Well, when they woke up with their packs rifled and a lot of nice crap I'd been meaning to remove from their inventories missing, they were, shall we say, disturbed.
Ranger tracked down little kobold footy-prints to a hole, and in they went.
Remember what Roger said earlier about not going where you can't stand up straight? HOW tall are kobolds? I assure you, they ain't digging their tunnels bigger so YOU can walk comfortably in to slaughter them. The big, burly paladin had to leave his plate back with the horses to fit in the tunnels. (Said horses did appear later, roasting over a spit...)
Tons of traps. Deadfalls. And, over it all, the sound of kobolds giggling...
I let one of 'em escape alive, to carry back the tale.
Was the closest I ever came to a TPK, I do believe that I shouldn't go out of my way to slaughter characters in which players have put time and effort... And, had they turned around and left at any point, I'd've taken a few more nonlethal shots at 'em for punctuation and let them go, without their stuff. But, "they're only KOBOLDS..."