I have a few keyboards here. As you can imagine I type a decent amount in my line of business.
I got a totally worn out Microsoft Comfort Curve 2000.
A Microsoft Natural Ergonomic 4000 (which I currently use). It's about 8-9 years old already. It's great.
A Corsair K65 Cherry Red (waaaay too sensitive keys). I should have gone for the Blue.
A Chinese made IBM clone keyboard (membrane, but satisfyingly clicky). I broke it though and I'm too lazy to get a new one. It was only US$3 though. It typed surprisingly well.
But nothing has ever come close to the great IBM Model M keyboard. The next best thing is this: Unicomp, Inc. Classic 101 White Buckling Spring USB
If I could afford the shipping I would get 2! I highly recommend these.