Well if you look on the main page you can see a lot of them are Dell, Gateway, ect. Over half of the main page units are proprietary units sold in prebuilt servers and desktop computers.
The Corsair TX, HX, and AX units are made by Seasonic who make some of the best PSUs out there. We (more so I) recommend them and only them really. Antec makes good units too, and the Thermaltake TP series is good, but I prefer to recommend Corsair to mostly everybody.