RFF is the main photography site I visit in the internet.
Sometimes LUF and lomography site, it's nice to see something different, even if not always I like the images.
Less frequently The Online Photographer and the Kirk Tuck blog, now on pause.
Flickr but not much, anyway I found interesting photographers to follow.
Magnum photos is a good place to spend some time, in my opinion.
A few days ago I stumbled in this site,
Emulsive which as preliminar view seems interesting.
Burn was a place I used to visit, but recently I have lost interest in it, not sure why.
For personal reason I'm not on FaceBook or Instagram which is a limit to the possibility to look for photos.
Generally speaking I prefer to look for the sites or blogs of photographers whose work I find interesting, as lamefrog said this can be done visiting sites od editors and looking for the sites of authors of the books,
Steidl and
Filigranes are a good starting point.