Mellow Mushroom is a pizza chain that I always thought was local to the Central Florida area. I found out this wasn't the case while up in Atlanta after our first food choice didn't work out. From their website, it looks like Mellow Mushroom spans pretty much from coast to coast.
Everyone seems to love this place though. I've never been to a Mellow Mushroom that wasn't busy, but there are definitely far better pies out there from independent places.