I mostly use mail-order labs these day, these are my favorites.
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.
North Coast Photographic Services
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.
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.