For nearly two years, I've been using the PC version of the Logitech diNovo Edge keyboard, and I've been quite happy with it.
I've always been a huge fan of the feel of the IBM Selectric typewriter keyboard - perfect keyboards, not too noisy, incredible feel with a definitive release. IBM simulated that with bucking spring technology of the original IBM PC and its follow-ons, and I used those keyboards too, and thought they were the best at the time.
These days there are some similar keyboards for the Mac, and I've tried them all, but never really liked any of them. The feel just wasn't right, and while they had a similar sound, they were just too noisy, or too 'fake' feeling. It's hard to describe, but... they just didn't work for me, and I kept going back to the Apple keyboard.
The diNovo Edge isn't anything like those keyboards. It's more like a very high quality laptop keyboard, but with much better "feel". It's got smooth travel -- and not too short, which is a common failing (see the Apple aluminum keyboard, which I've also tried) -- a good 'release' feel when you make contact (but before you bottom out on key travel, and good layout. (It feels similar to the original IBM Thinkpad keyboards, if you've ever used one of those.)
Unfortunately, while it worked, it wasn't really made for the Mac, and you had to play some games to get it to function. But I liked it enough to recommend it back in November of 2006.
Well, this week, I replaced that keyboard with the new Logitech diNovo Edge Rechargeable Bluetooth Keyboard for Mac. (And it has an awesomely catchy name. Not.) They've reworked the key layout, improved operation, and written Mac drivers that work well and activate various application-specific keys. Plus, it has built-in rechargeable batteries that last about 30 days per charge, and comes with a little dock charger thingy.
No, it doesn't clack. It's not a selectric. But it's got a good feel, nice (adjustable) flat profile, excellent build quality and -- to my hands, and in my opinion -- it's the best modern keyboard out there.