If you're in a creative rut or maybe just looking to kill some time productively, I suggest looking at some of the photos from the giants of the field. I think we get so wrapped up in our own work at times that it's good to take a step back and look at other work once in a while. And don't just casually flip through a book or a website. Spend some time looking at a photo you like. Give yourself at least 5 minutes with a picture and try to figure out what about it moves you.
Look at the light, the lines, the composition. Really try to See what it is about that image that speaks to you. And don't just look at photos that are similar to the subject matter you like to shoot. If you shoot landscapes, look at portraits, still lifes, etc. and try to bring those ideas back to your own images. How would you shoot differently if you shot that leaf on the forest floor as if it were a person's face in a portrait?
While it would be nice to have shelves full of beautifully printed monographs to look at, one of my favorites sites for this exercise is Photography Now. Here you can view the masters along with contemporary photographers in a beautiful book-like format. Give yourself some time this week to stand on the shoulders of giants.