Just about any cog will thread onto a track hub. It's the lockring that has different threadings. EAI, Dura-Ace, and Suntour all have flawless reputations. Surly is also good, but their model hasn't been around for too long yet, so word hasn't gotten around yet. The new IRO's look like Surly's. Soma's are reportedly crap.
Except for the EAI and Surly, this post is all hearsay.