I never used SmugMug but heard only good things about it, just like Pat says. I use Zenfolio and it costs $100/year for a professional account with unlimited space that allows you to sell your photos without moving a finger other than uploading and set prices. You can also redirect to your own domain name with the pro account so that the name Zenfolio does not show.
Cheaper accounts start at $29/year I think. It's a great site, quick and professional looking.
I'm still working on mine, haven't had much time, here's the link http://lucadiana.zenfolio.com
On a last note, many of these sites allow referral which saves money to the person referring and the person referred so before you sign up make sure you talk to one of the people who have the site of your choice.