I dive a Gorski G2000SS...the latest model. I am very happy with my hat. Major design flaw is that there is no "dial-a-breath".....easy to remedy if you have a screwdriver and 5 seconds on deck. Can't dial out on the fly though. Other than that, the Gorski is a bad ass hat and it is damn near maintenance free.
There are plenty, depending what you wane do / job to be done.
for inshore: Desco airhat, see Desco site, advantage of this hat are the cheap maintenance costs, approx <100 dollar/year instead of the (over?)priced KM-spares....
As stated bellow, the Gorski, or a Gladiator are both decent replacment for the KM's series.
Desco also got a deepwater hat similar to the KM serie, ref to Desco - site.
For light work, AGA mask or GSD400 (that one is out of production but still several (new) mask on the market.