1) The biggest hit was what I called a "spider feeder" -- a 10'x10' spring-loaded trap door hidden by dusty ground, which acted as a catapult to send a triggering hero up 10' into a web-covered ceiling while reveaing a 10' pit beneath them. The PC was then forced to make a choice -- make a skill check to disentangle from the webs and fall 20', or remain in the web? One turn later comes the deathjump spider. Oh, and where's the door? Now it's a 10'x10' wall dividing the battlefield (disabled with a single Thievery check or two attacks to cut ropes). That was fun.
The fun of designing was getting into the kobolds heads and thinking of how they'd use their home environment and nearby materials...
2) The kobs had another trap I called a "zombie pusher", which they had originally created to keep undead from a lower level from climbing up to theirs. Turns out it conveniently doubled as device to propel intruders from their lair into the zombies' domain. Picture it as a hidden bundle of thick logs wrapped in rope attached to a dark high ceiling (conveniently covered by webs). It activates by tripwire, swings down to slam into PCs and knock them down 20' into a nest of zombies.
Hmm..what else?
3) Slime-coated slopes. The kobolds laired in a cave complex that had a fetid pools of water accessible by mutiple tunnels. They coated the 40' descending slope of one such tunnel with cave slime. If, during a fight, creature were to fail an Acrobatics check after being pushed into a bit of the slime, they would then slide 8 squares and splash into a big pool of possible filth fever. They'd then have to spend about a turn swimming and coming back around to the battle's main chamber. Get a disease, lose a turn. Good times.
Anyway, those are three. I hope they serve to inspire. I got my inspiration from staring at the dungeon map and thinking -- who do these kobolds live with? What's nearby? What do they know about their home that their intruders wouldn't? What qualifies a trap to them?
You've got a black dragon to work with...that's a big something. Perhaps a trap give intruders' presence away to that dragon sooner than they'd like? Fun with acid?
As for "cheap shots", I say go for it. Kobolds are shifty little turds. They're all about cheap shots and you should push that feel. Keep the DCs for passive Perception fair, let them know that rolling Perception is an option, and all will be well.
I've babbled on enough -- please share what you come up with! 
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