The keyboards that Apple has produced for the Mac over the years have all been pretty good products. But their high price puts many of us off when it comes time to replace a keyboard due to a failure. In my case, it's almost always the fault of one of our cats. (No, really; would I dare blame a cat if it weren't true?)
I usually look to third-party USB or wireless keyboards when I need a replacement. I've used keyboards from Logitech, Microsoft, and many others, and I haven't had any problems with any of them. There is a small difference between them, though.
Keyboards designed for the Windows OS don't have the same keycap names as Mac keyboards. All the alphanumeric and punctuation keys are there, but you won't find Command, Option, and a few other keys that you'll find on a Mac keyboard.
That doesn't mean they're not on the keyboard; they just go by a different name. If you want to use a Windows keyboard, this guide will tell you where to find those missing Mac keys.