Rainwalker made me a great IWB Kydex sheath before. He does IWB in leather too and he is really a master at his craft <img src="/ubbthreads/images/graemlins/thumbup.gif" alt="" />

Like Skunk said, you can't go wrong with any of the experienced kydex benders. I have a few sheaths from AZWelke that are top notch, So are Mashed Cat, Steelnut, and Okuden. I've never had a Buy Brown sheath, but I'm sure they are great too.

If the sheath maker you choose doesn't offer an IWB option, you could always buy a comptac clip and attach it to the sheath yourself: http://www.comp-tac.com/product_info.php?products_id=81&osCsid=aq21h6ig7jg652oe8akftqgk70