"crocs, the universal symbol of men who have given up hope"
sperry top-siders for scrubs, pumas/converse/other retro looking sneakers are also acceptable, maybe toms...
cute flats for all other days--banana republic probably has the most comfortable ones, and ivanka trump's are classy, but I've also had success w/ bcbg, jcrew, nine west, urban outfitters and topshop. In med school I had the most amazing pair of Loeffler Randall for Target flats that I wore down to the bone and I've seriously considered starting a petition for them to reissue them.
Oh, and don't forget a great pair of flat boots for the colder months.
Dansko's should be banned.