I posted on this forum a little while ago, just started using them, I mail them about 6 rolls a month and they're fantastic. I don't get my slides mounted, I prefer to scan them, but $5 cannot be beat, even with local shops where I wouldn't have to pay shipping.
In Philadelphia, there's Philadelphia Photographics: http://www.philadelphiaphotographics.com/ They offer everything from E-6 processing to optical RA-4 prints. I have used them a few times and have always been impressed.
Another NYC choice is CRC on west 22nd street near 6th ave, right next to calumet and across the street from fotocare, they do all my non b/w processing and I get excellent results every time, they have a great staff, and very fast turn around (if you're down in the city for just a day, drop off e6 or c41 at 10 am and it'll be ready by 1 pm at the latest, usually.)
Another NYC choice is CRC on west 22nd street near 6th ave, right next to calumet and across the street from fotocare, they do all my non b/w processing and I get excellent results every time, they have a great staff, and very fast turn around (if you're down in the city for just a day, drop off e6 or c41 at 10 am and it'll be ready by 1 pm at the latest, usually.)
CRC is my main processing lab. I've never had a problem there nor any mix-ups. The staff is friendly and professional. Also, they offer a 30% discount for students.
Duggal is hit or miss in my experience.
I've heard good things about LTI on 30th between Madison and Park Avenue. I've never been there though, since I'm so used to going to CRC.