Yukon just came out with a new Air Locker they call the Yukon Zip Locker. The "Zip Locker" is very similar to ARB but will cost you less, competition is always good and may even drive down prices on ARB Lockers. Word is the new Yukon Air Locker will be selling for about $659 and I'm thinking seriously about giving one a try. If you break it you just take your handful of parts to them and they give you a new Locker!

Yukon also has several other lockers out including the "Grizzly Locker" which is similar to a Detroit Locker, The "Duragrip" LSD type unit, The Traction-Loc, and the Powr-Lok. You can see more details at Yukon's site here; http://yukongear.com/Positractions.aspx

The internals are forged 4320.
The units themselves are assembled in the US.
They are all 4-pinion design, with the exception of the Model 35 unit, which had to make allowances for c-clips. The smaller units such as a Dana 30 and Model 35 will be safety wired to deal with the housing flex issues that can loosen cap bolts.

Here is a complete installation done by AllJeep with pictures;
http://www.alljeep.com/tech/ziplockerinstall.htm

http://yukongear.com/

http://www.ringpinion.com