Eventually, over a long enough timeline, you will end up having all of the controllers. You might as well buy them now!
Harmony remote - so you can have only one remote. It has dedicated WMC IR codes already, if you use WMC. (disclaimer...wife and kids don't seem to follow directions, a lot, then they claim the "remote didn't work again.")
Logitech K400 keyboard - small-ish and functional, stashes under couch easily
Lenovo N5902 or N5901 - alternate keyboard/mouse. Small and annoying, but small.
Flirc - IR receiver that allows you to "program" any remote button to do any keyboard function. With this, you may not *need* a harmony.