For a few months now I've been happily using a Gyration Wireless Keyboard and Mouse for my Windows Media Center. I've been extremely happy with this combo. The mouse can be used without needing a table or surface (you just wave it in the air). It takes a while to get used to this, but once you do then you are free to walk around etc while you control the mouse. The mouse comes with a charging station and also has an optical sensor so that I can be used as a regular mouse.
They keyboard is very small, and is running on it's original set of batteries. It's perfect for MCE as I can easily hide it. Another bonus is that the keyboard requires no drivers and works on the BIOS screen in case you need to make any tweaks etc.
A few weeks ago, my mouse flaked out though. On Monday I finally got around to calling them. The support experience was fantastic. I got a human on the first ring and he told me to send it back to them (no need to find my receipt or anything). Today I got my replacement (total of 4 day turnaround). Now that's great service!