Manufacturers with great customer service

Aric Audio, Coda, and Cerious Technologies. All three provide exceptional pre-sales and post-sales support.

Lampizator of Poland has outstanding customer support

Small Green Computer and Bricasti have been super.  Over 40 years ago a crack developed in my Ortofon Concorde 30 cartridge.  I contacted them about it via snail mail and they returned a new cartridge to me no questions asked.

Veritas Cables: Already on saw it on this list a few times, but the team at Veritas Cables has been amazing to deal with. Very fast and patient with my never ending stream of questions.

ModWright: Also already mentioned a few times, but Dan at ModWright has always offered exceptional service. 

HeadAmp: While they now resell many other brands, HeadAmp started as a manufacturer and continues offering truly special headphone amplification. Justin goes out of his way to give great advice even when dealing with second hand gear he built ages ago.

Tiglon USA: A new one that I've been really impressed with the past few months. Again, going the extra mile to make sure the customer is totally taken care of and comfortable with the transaction. Highly recommended.