I'm still using IBM Model M's on all my home and work desktop PCs. I have a good supply stashed (from ebay years ago), though I've hardly had to dip into it. Most PS/2 -> USB converters would not work with the Model M, so once I found one that did, I laid in a supply of those as well. Will pass the stash on to my kids if they're interested...
Edit: for extra credit: I'm still using the Logitech Optical "Marble mouse" (trackball, really) which I switched to (again, on all home and work desktops) perhaps 10 years ago when use of a standard mouse led to acute arm and shoulder tightness and ache/pain. I remain pain-free in this regard since the switch. Maybe any other trackball would work just as well, but this one did the trick for me. BTW I use an HP DV8113CL laptop with Synaptics Touchpad extensively and I'm happy with it (though the keyboard is merely adequate). I've had occasion to use IBM trackpoint's (including those built into IBM Model M's as well as Thinkpads), and did not like them one bit.
I use a Lenovo Thinkpad keyboard. They're widely accepted as the best laptop keyboards, but also available as a USB device for desktop use. I find a short-stroke keyboard less tiring and like having a consistent experience across desktop and laptop. The trackpoint is very useful for keyboard-dominated workflows where the mouse is used only occasionally.
Trackpoint is actually more accurate and efficient than mouse. So even if you shift to mouse-heavy workflow for some tasks, it's not a problem. Unless you're not really familiar with trackpoint (or you're unlucky and drifting problem is hitting you often, but that's another story).
I am happy with Apple keyboards (both external and those they have on notebooks), but whenever someone starts a discussion about keyboards I show these: http://www.daskeyboard.com/ (check out the ultimate). Alas, never saw or tried one myself.
I own a DAS Keyboard Professional which has Cherry blue switches (http://en.wikipedia.org/wiki/Keyboard_technology#Mechanical-...). I love the way it types and I love the sound it makes, but if you asked me how much more productive it made me then I'd answer zero percent. The only time I actually need to type a lot (and fast) is when I chat with co-workers about project-related questions.
I use a Kenesis Ergo keyboard - super comfortable to use for long periods of typing, and great if you have any issues with (or concerns about getting) RSI.
I bought one for work and liked it so much that I ended up getting one for use at home as well. (Which given the cost of the things is saying a lot =)
The other advantage (at least in a work environment) is that other people are less likely to want to use your computer when you're not there, (and even less so if you use the built-in dvorak remapping)
My favorite is the Kinesis Evolution chair-mount, but you can't get them anymore -- they stopped making them a few years ago, and even the eBay supply has dried up.
I am personally very fond of the Unicomp Customizer. It's relatively cheap for a buckling spring keyboard and very no-nonsense (it has just what you need, no more no less). I must say that, much like pencils, once I went mechanical I never wanted to go back. http://pckeyboards.stores.yahoo.net/customizer.html
I switched to http://typematrix.com keyboard about 5 years ago when my wrists started hurting. I've been happy with that decision. The unmarked one I purchased at first really made me focus in my touch typing.
One downside: When I go to a co-worker's computer with a normal keyboard I feel like I can not type.
Best laptop keyboard I've used is the one on my old 12" Powerbook G4. I can just fly typing on that.
I had a Happy Hacking keyboard for a while, and it had a nice feel but I eventually decided it was too minimalist. I sold it on eBay for nearly what I paid for it new.
I'd like to find a Model M to play with for a while; haven't used one of those since the 1990s.
In the stackexchange thread someone pointed out that no num-pad means a shorter distance to the mouse. I really like the idea of that (I used a wireless no-numpad apple keyboard for awhile) but I also really like the functionality of the num pad. What's a good compromise?
I was looking for a keyboard without an attached number pad that wasn't ridiculously expensive. I settled with the Microsoft Bluetooth Mobile 6000. I don't need the external number pad, bluetooth, or curve but I don't mind these.
It's a solid feeling keyboard despite it's short keystrokes. I'm glad that Microsoft didn't mangle or rearrange the left control and alt keys. The home-cluster and arrow keys are squashed and partially relegated to functions, but I think this is a worthwhile trade-off. Between vim/emacs and the shell, there shouldn't be too many reasons to use these keys anyways:)
My keyboard (Logitech DiNovo edge, I find keyboards with no tilt and short travel vastly preferential for speed and carpal tunnel) doesn't have a numpad, for those rare occasions I need one I have a dedicated number pad plugged in - it's a USB keyboard, just only the numpad part.
The MS X6 lets you move the numpad to the other side of the keyboard (or possibly leave it detached, but for mouse access those are equivalent options). I don't have one, and it's reviewed less favorably than the X4 which doesn't have the removable keypad, but it's something.
The shorter distance to the mouse is one reason I prefer laptop keyboards in general. The trackpad is centered below the keyboard, and it's always in the same place relative to the keyboard, reducing the slight time it takes to find the mouse on a conventional keyboard setup.
I like different keyboards, from the wireless Apple to the Model M. I use the Apple now because its small. Is there was a cheap Model M (not the 200$ happy hacking) around this size (no numpad etc) and wireless...
Around 1999, my first Kinesis Classic saved my career. Switchover takes a bit of retraining of muscle memory, but I honestly cannot say enough great things about these keyboards.
Edit: for extra credit: I'm still using the Logitech Optical "Marble mouse" (trackball, really) which I switched to (again, on all home and work desktops) perhaps 10 years ago when use of a standard mouse led to acute arm and shoulder tightness and ache/pain. I remain pain-free in this regard since the switch. Maybe any other trackball would work just as well, but this one did the trick for me. BTW I use an HP DV8113CL laptop with Synaptics Touchpad extensively and I'm happy with it (though the keyboard is merely adequate). I've had occasion to use IBM trackpoint's (including those built into IBM Model M's as well as Thinkpads), and did not like them one bit.