I don't think there are any DRM-free recorders out there, unfortunately...but there used to be a way to strip the DRM from the recorded files using software called DRMDBG and FreeMe2.
The way I used to do it is run DRMDBG to get the key, then FreeMe2 to convert the file into a plain DRM-free WMV.
The latest version of FreeMe2 is here:http://sourceforge.net/projects/freeme2/
DRMDBG is a bit harder to find, and you would need the latest version...and honestly I'm not sure what that is.
Another option you may find easier is recording HD content with component video, which has no DRM flags. It's only the digital recordings that have these limitations...but you would need a way to run component video from your TV box into your HTPC for that to work. Obviously, the recording would need to be done with a video capture program and not media center, so this wouldn't be the most convenient solution.