I use Wal-Mart for all of my processing, unless I'm doing test rolls, in which case my local grocer will do. My local grocer is guaranteed to scratch my negs though.
I've sent Kodachrome, E-6 in 35mm and 120, C-41 in either size, and even regular B+W in 35mm and 120(e.g. Ilford Pan F), and they seem to do it all for really low prices. I think a roll of 120 negative film developed with 4x6" prints from my Zeiss Super Ikonta C costs me about $2.00. Less than $3.00 anyway. I know they send Kodachrome to Dwayne's but I don't know about the others - I think Fuji labs does them.
With 35mm slides however, they always seem to insist upon mounting them in cardboard, even if I request no mounting. With 120, they return them sleeved.
I tried to ask them to push process a roll of E100Gx by two stops as I shot it at ISO 400 instead of 100. They returned the roll, stating that they don't push/pull process.
I've never asked them to scan, as I do my own 35mm scanning with a Nikon CS5000.