The first tutorial is from cssplay and is one of my favorites around. They have a very elegant and simple image gallery. Your images are separated into different sections (people, plants, animals, etc) and all your images for each section listed nicely underneath. As you hover over each image it expands double it's size so you can take a better look at each image before you view the full version. The interface is very clean and simple to use, I recommend taking a look at this one.