Manufacturers with Excellent customer service

Beyerdynamic headphones.

Cerious Technologies Cables.

Deja Vu Audio though they are a dealer that manufactures rather than a straight manufacturer.

Audio Note UK.

I'm sure there are a few others I am forgetting I'll add on if I remember any.

My experience with Pass Labs was exemplary.  I called them and a guy answered the phone and spent ten minutes or so with me discussing my issue and patiently answered all of my questions.  At the end of the conversation I thanked the guy and told him I appreciated his help....and I asked him what his name was, he replied "my name is Nelson Pass."

Another time I called them to ask the price of a power cord for one of my X-600 monoblocs....they sent me one for free.

I've had great experiences with Audio Research also.

Another nod for Modwright
Will add Daedalus Audio & Mojo Audio

Best:    ARC, Ayre
Worst:  Audible Illusions

Jiun-Hsien Wu - MHDT Labs
Paul McGowan - PS Audio
Mark O'Brien - Rogue Audio