we use smugmug. it's not bad but the pro account is a bit expensive if you don't intend to use it a lot. we've ordered prints from them and the print quality is pretty good. our clients don't seem to have any complaints about the print quality or service from them either.
what happens with the ordering process:
1. upload pictures (high or low res)
2. send link for gallery to client (can be password protected)
3. client orders prints
4. you get an email telling you they ordered and you need to proof the order
5. if you uploaded low res images then you get to replace them with high res at this point in time. you also get to check the crop that the client chose. if it's not a good crop you get the change it to avoid chopped off heads and what not.
6. after you're done proofing the order just submit it and you're done.