If you're in US then you have RennTech in Florida or Evolve in Chicago area. Both are world known tuners that offer excellent remaps for gas or diesel.
Retired: 2005 N52 E90 330i Sport 6AT
Retired: 2007 N54 E92 335i Sport 6AT
Current: 2012 M57 E70 X5 xDrive35D