My KA-BAR TDI Law Enforcement Straight Edge Knife... When I am conceal-carrying my Ruger LCR behind my right hip, I wear this knife behind my opposite (left) hip. Mainly as an alternative/backup form of protection, but also in case I were to ever get into a struggle and the perpetrator were trying to grab my gun. I could then hold my gun into its holster with my right hand, while using my left hand to grab my Ka-bar and defend myself... It came with a kydex sheath that makes it easy to un-holster and re-holster without cutting myself, and it is also surprisingly comfortable to wear.
You can switch it around any way that you want, so it can easily be worn IWB (in the waistband) or OWB (on the waistband). Normally I prefer IWB b/c I can easily slip my shirt right over it, allowing it conceal quite a bit better.