I'm going to go out on a limb and say a k340 or even a k240. Sweet sweet sweet midrange. The 340 will take a beefy setup to milk the most out of it, though. The 240 will sounds pretty darn good right out of an ipod.
You might not want the k240s, though, its a bit on the muddy side. You won't know unless you try though. You are welcome to auditioning my k240s, if you'd like.