There are many DRM removal tools. The list is not limited to Soundtaxi and it clones: WMA Convert, MelodyCan, TuneCab and TuneRaft.

Anyway you shouldn't remove DRM from rented files.
DRM removal software is intended to be used on legally purchased files.

FairUse4WM and freeme2 are free programs that can remove DRM from Windows Media .WMA audio files and .WMV video files. Many people use them 'coz they offer better quality than lossy programs like Soundtaxi. However these free tools are not so easy to use. It really depends on you what to choose.