By far the best i've tried (and i've tried a lot)
http://www.4photolab.com/
I live in Rochester so just drive over to drop off my film to them. A little pricey but the quality is steller. I get all my 4x5 and E6 slides done from them. I'ts easier and cheaper to drop off the c41 at the local walgreens. Praus will do almost any film (including infared etc) clip tests etc. If you just want to do C41 it would be cheaper to find a target/walgreens that have a high volume. I simply took a few exposed rolls drove around town to the various walgreens/rite aid/ wallyworld etc and tried them all out before settling on one.