An RF remote control is a great addition to any Home Theater PC and the ATI Remote Wonder II is a great choice. Unfortunately it isn't sold new any more so you'll have to purchase used (it's available on Amazon used or EBay. Further the setup for most HTPC software programs might take a little extra work. Fortunately David Vielmetter has a nice how-to on setting this remote control for SageTV.
"Rather than depending directional infrared signals, it operates using x10 radio frequency signals (~433 Mhz) that can penetrate walls and greater distances than infrared. This makes it much more responsive than than traditional remote controls especially in situations where you need repeating signals. Up until recently I had been using a SnapStream Firefly RF remote control, but after 2 years of use its performance degraded to a virtually unusable state. So I picked up this ATI Remote Wonder II on eBay for $15 and so far it has proved to be a great replacement for my HTPC running SageTV. Here’s how I configured it..."