It's a bit of an irony that I'm here to say don't buy the (still excellent) Mac keyboard, since I made the original recommendation for the Mac keyboard. But I'm using a Logitech K810 now, and it's spectacular. It's beautiful--brushed metal like the Mac keyboard, but much darker like nickel or gunmetal. It's approximately the same size as the Mac keyboard, has a perfect layout and is a joy to type on. But what really sets this thing apart is that it has three Bluetooth buttons up top, each representing a separate profile. So, for example, button #1 is associated with my main PC, button #2 is associated with my media center PC, and button #3 is associated with my iPad. To disconnect from one device and connect to another, I just tap a single button--no silly removing of devices and going through the whole discovery/pairing process. It's actually got some other features that I don't really think about, but are nonetheless awesome. For example, the backlight only comes on when needed (ambient light sensor), and there's a hand-sensor so the light comes on as your fingers approach the keyboard. This is cool on its own, but it also improves battery life pretty substantially.
Also, and this is the biggie, it's great for Windows 8.