Since the Input Devices in under construction, may I take the liberty of recommending the Microsoft Media Center IR Remote and Keyboard combo.
I have used other Radio Wireless Keyboard and Mouse combos in the $60-$80 range, (including the Microsoft Wireless Optical Desktop and low end Logitech Keyboard and Mouse Wireless Combo) and have been largely disappointed at the reception performance.
For $60 Canadian, I was able to find the MCE IR KEyboard and IR remote. I coupled it with a Logitech G7 mouse. The results were remarkable. IR transmission from the MCE combo always successful even without LINE of SIGHT!!!! It will work as it's not covered by a blanket and as long as your in the same room. The IR must be VERY bright!! Most of the time the wireless radio combo didn't work in the same room!!!! As for the Logitech G7 Wireless mouse, it works at the 2.4 Ghz band, there has never been a problem with reception either even with WiFi, but your paying $100 Canadian for it.
As for controlling the rest of the home theater system beyond just the HTPC, I would HIGHLY recommend an activity based universal remote. I was able to grab a Logitech Harmony 659 off Ebay for around $60. First Activity Based remote I've used let me tell you, I don't know how I could have lived so long with the dumb universal learning remote that came with my Onkyo Amp where you had to tell it what device you want to control before actually being able to control it.
Perhaps the best remote for that price range.
I've seen some remotes at $500 range, but besides more buttons and a bigger LCD, the fundamental functionality remains the same in all Activity Based Remotes, so just buy what you need.