Quaife makes what is in my opinion the best one, but it is also the most expensive. It is what I have in my car.
You can also pick up an Integra Type R LSD from Japan. Watch Ebay or someplace like that and you can find them for $300 to $400 each. Probably not as good as the Quaife, but still damn good
Mugen makes one, but it is really fucking expensive, like $1200 and no better than the Quaife for less.
If you are looking for a clutch type diff I think Kaaz makes one too, but I don't know much about them.