The IBM model M, and its predecessor the model F, are considered classics among computer users. They use what's known as "buckling springs" in the key-switches, which give them that nice, solid, click-y feel. Another user of them are the old Northgate keyboards from the '80s and early '90s. Here's a sound sample of me typing normally on my Northgate Omni-Key keyboard:

http://www.electronixandmore.com/ada...hgate_demo.mp3

Apart from those, the Commodore "breadbox" VIC-20/C-64 keyboards are also nice, as are the ones used on the early Apple II series machines (as well as the Lisa). Not quite as solid as the "buckling spring" ones, but they have a great feel, and are usually still working flawlessly 30+ years later. As for least favorite keyboards, the "membrane" keys on the Sinclair ZX-80/81 have to be up there, along with the rubber "chiclet" keys used on the Mattel Aquarius and the original TRS-80 Color Computer. Not quite sure what they were thinking on those...
-Adam