Is there some online collection of really great photos of great photographers, maybe with some comments giving hints on the reason of their greatness?
If you want well-known masters of photography, then here are two sites.
Profotos has a lot of narrative about the photographers, with links to photographs.
Masters of Photography has a lot of images, but the site is littered with pop-up ads, so may put you off
Atget Photography is a good combination of image galleries and short biographies on a number of master photographers. It also includes links to worldwide museums and galleries.
500 Photographers Blog!
What genre of photography do you like? There are SO many photographers out there. Also, visit your local art school, and go to their library, visit photography section, get some coffee and get going...