I think that John Shaw's photographs in his photo books are useful to look at. Donald Miller's photos on the gallery are instructive. Inernet galleries of famous photographers are helpful. I like all the Ansel Adams books. Also, zipping through the APUG galleries allows you to quickly see what catches your eye and what does not. Then slow down and study why that is so.
Of course, some of this just depends on what you like. For example some people seem really excited about muddy platinum prints or random pinhole camera shots. Likewise ULF contact prints with minimal depth of field and bokeh. To each his own but if you study what you don't like you can learn also.