Mechanical manufacturer Cherry seems to make the most popular mechanical keyswitches these days, and there are several kinds which are named by the color of their stem:
The original Das Keyboard uses Blue Cherry keyswitches, which produce a very loud click sound when the relay connects, which is quite nice sometimes but can make cube enemies fairly easily as well. The Model S Pro Silent uses Brown Cherry keyswitches, the same as used in the Filco Majestouch Tactile Touch keyboard.