Interactive visualization of how different camera settings affect overall image... Do you know how changing settings (Shutter speed, aperture, ISO, etc) affect exposure, depth of field, focus, and grain texture? This site will help you understand those relationships and better control them in your own work.
Concentration Idea Lists... You know how to Google things. Have you tried Googling up some ideas for Concentration topics? There are a lot of examples out there- Here's a good one. And here's another good one.