I offer you what i consider are the best keyboards for emacs. They very in price, built quality, size. Some have mechanical keys.
First two is Microsoft's ergonomic keyboards, the Microsoft Natural series. They are cheap, under $40.
These are classics. Particularly nice is their huge Alt and Ctrl keys placed symmetrically for left and right hand, and very close to the thumb. The 4000 is the later generation. I used them since 2005, 3 years with the classic and 2 years with the 4000, but finally gave up on the 4000 and switched back to the classic. The 4000 got the problem of stiff space bar.
Now, comes these 2 bowl-shaped oddball.
They are more radical, and expensive, about $300 for Kinesis and $500 for Maltron. I've never used them. The bowl-shape makes it less ideal for casual use.
The Kinesis screwed up the function keys {F1, …, F12} and Esc. They became rubber buttons.
Maltron is ugly, and much more expensive, but i think it's functionally superior. It has good function keys. For each thumb cluster, it has one more key. And the middle matrix of keys, you have multimedia keys and number pad if you need it. If you don't need it, they can be used for extra function keys. All single button press to switch to {browser, emacs, workspace, windows, apps}.
The Maltron is good as a power station. See: Keyboard Master: One Thousand Function Keys.
Both use mechanical key switches. 〔☛ Guide to Computer Keyboard Key Switch Mechanisms〕
Next, we have the “Truly Ergonomic Computer Keyboard” and μTRON.
These are less radical, but i think they are the best. The TE is comparative inexpensive, at about $220. The μTRON is over $500, and is split into 2 physical pieces, and you have to buy in Japan (or Amazon Japan). Both use mechanical key switches.
I currently use the TE and love it.
In summery, i think these are the best keyboards for emacs. If you want compact, the TE is way to go. If you want split pieces, the μTRON is for you. If you want bowl-shaped, then Kinesis or Maltron. If you want it cheap, then Microsoft Natural.
You'll notice that they are all split, ergonomic types. I recommend them highly. But, if you really just want a straight keyboard, then i recommend Logitech G710+, Corsair K60, K90, or Filco, Cooler Master. They all feature mechanical key switches.
Also, i don't recommend laptop style flat/shallow keys. Some of you will probably mention TypeMatrix, or IBM Model M, Unicomp buckling spring, or Happy Hacking Keyboard. Then, there are also other 2-Piece Split Keyboards. I'm sure they work for each person, but i wouldn't consider them under the title of “best emacs keyboards”.