My all-time favorite is the Cherry G80-3000

While the G81 and G83 models are not much different from "cheap" keyboards, the G80 models are really high class in terms of quality.
Take a look here: http://www.cherry.de/english/business-solutions/office_business_g80-3000.htm

This keyboard is available in various versions, e.g. with three different key characteristics ("Linear action", "soft contact", "keyclick").; the version for PS/2, Win, linear action (which I prefer), German layout is the G80-3000 LPMDE.

Greetings from Bonn,
Roland