I have my E-6 developed at 'Color Services' in Needham, MA. They develop same day and you can drop off/pick up or handle it all via mail. They offer 35mm up to 8x10. Great place, nothing but awesomeness from them.

I've used Dwayne's in the past and they have done an excellent job, as always. But more recently, I've begun developing my own slides. I leave them unmounted and store them in archival pages.

Developing slides is not hard. The only challenge is keeping the temperature of the developer withing one degree F or so of the correct temperature. Since the preferred temperature of the developer I use needs to be 105F, I use a styrofoam container to hold the water bath. Sometimes I have to add hot water to the bath during development. What I usually do is bail out a cup of water and then add a cup of hot water. I get better results doing it this way.

Oh, and speaking of results, they have been great. So, not only do I get to develop my slides without having to wait for the turnaround, but it's also a lot cheaper to develop my slides at home. And the quality of the images has been excellent. I buy my kits from Freestyle.