The IBM Model M is not a relic of the past. We are using around 15 of them at Wendell's shop alone. They are still used today (especially by programmers) and I would wager their popularity is increasing. If you use one, let us know in the comments.
A lot happens when you press a key onthe IBM Model M. As you press down a spring compresses until it buckles, triggering a hammer which hits a membrane. The Model M is clickier than just about all of the modern mechanical keyboards. Check out the video for a sample of the clicky majesty.
This keyboard might last through a nuclear war. The steel back plate makes it heavy (around five lbs), and it is insanely sturdy for it. Also, each key has a separate hole containing a spring and the membrane. These holes are virtually sealed. Today, most keyboards allow the dust to go where it pleases. The dust gets into the Model M, but it won't effect much.
Where to Buy
If you want something shiny and new, complete with a Windows key, check out Unicomp. They own the patent on buckling spring style keys and they still manufacture Model M clones. They can also create custom keyboards for you, but you will have to cough up quite a bit of loot for one.
If you want a Model M you should search Ebay. They come in various states and if you find a good one you should expect to pay over $40. If you like clicky keys, you should be jumping at one of these for $40.
How Will I Live Without the Windows Key?
You won't have to... But that caps lock key must die! I hate the caps lock key anyway. It's the most useless key on the keyboard and it gets in the way more often than not. What I have done is map my Windows key to caps locks. This can easily be done applying a quick registry fix. I have the reg file at the office and will upload it tomorrow morning.
This is the keyboard that I use for just about everything. I occasionally switch to a mechanical gaming keyboard as they do seem to be a little better for gaming.
If you want something durable and you like mechanical keyboards, I'd recommend you grab one of these. If not, get one for the novelty factor.