I mostly use mail-order labs these day, these are my favorites.

 

Sf

Photoworks San Francisco

San Francisco, CA

Photoworks SF is my closest pro lab and I have sent E-6 color slides, B&W negatives, C-41 color negatives, as well as E-6 destined for cross processing to them without a hitch.  They work with 35mm through large format and happily deal with do-not-cut and other special requests just like anything else.  Their print quality is top-notch and they also offer free mailers.

 

Ncps

North Coast Photographic Services

Carlsbad, CA

NCPS is my favorite for when I want top-notch scans straight from the lab.  They develop color (C-41), Black & White, and slide (E-6) films as well as offer traditional optical and digital color and B&W printing.  What seals the deal for me is their excellent quality enhanced scans which provide high resolution JPEG files along with your film and prints.

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The Darkroom

San Clemente, CA

I like to use The Darkroom for processing film from our “toy” cameras: Holgas, Diana, and especially my Sprocket Rocket and my DSW’s Blackbird Fly.  They have a special service to scan & print your film including the sprocket holes which is a must for the latter two cameras.  They offer free mailers to send film to them, and also give you online access to your scans as soon as they are done.