One of the sites I HAVE to stop in at on a daily basis is Sushicam's Picture of the Day.
SushiCam photographer Jeff Laitila provides a stunning picture, big or small of daily or showcase life in Japan every day. It gets the honor of being my very first (top-most) RSS feed in my feed reader.
Another photographer I admire who publishes pictures frequently is John Watson and he maintains his site lightproofbox with a stream of wonderful pictures. He has a lot of other fun sites as well such as Photodoto (photography blog), FlagrantDisregard (life with kids) and fd's Flickrtoys (tons of fun things to do with flickr).
So with these in hand, I went looking for some other quality POD'ish (picture of the day) sites:Wikipedia:Picture of the day
Japan-Guide's Picture of the Day
Mainichi Daily News (Japan) Photo Journal
Mainichi Daily News (Japan) Photo Specials
NASA Image of the Day Gallery
National Geographic Photo of the Day
Not quite POD but cute and fun: Little People - a tiny street art project
I know there are a lot more such sites out there. What are your favorites for providing high-quality frequently rotating images?