In my search for more cases for Titan II, I found some OEM cases at this online retailer.
HTC Titan II Hard Shell Case - Black Original OEM 70H00538-03M
HTC Titan II Hard Shell Case - Silver Original OEM 70H00538-04M
HTC Titan II Hard Shell Case with Kickstand - Black Original OEM 70H00538-04M
HTC Titan II TPU Case - Black Original OEM 70H00537-03M
HTC Titan II TPU Case - Red Original OEM 70H00537-05M
I had the OEM hard shell case for Rezound and it was pretty good IMO.
HTC Titan II Hard Shell Case - Black Original OEM 70H00538-03M
HTC Titan II Hard Shell Case - Silver Original OEM 70H00538-04M
HTC Titan II Hard Shell Case with Kickstand - Black Original OEM 70H00538-04M
HTC Titan II TPU Case - Black Original OEM 70H00537-03M
HTC Titan II TPU Case - Red Original OEM 70H00537-05M
I had the OEM hard shell case for Rezound and it was pretty good IMO.