A very useful Facebook debugger tool where you can check how your webpage looks like on Facebook when like button is pressed, without actually pressing the like button.
Simple yet very useful Gimp tutorial where we make a detail or an object in a Photo bigger and more visible by resizing it and adding a white rounded square frame around it.
Often in PHP you want the same block of code to run over and over again and instead of adding several almost equal lines, you can use loops to perform this task much easier.