I have been coveting Copic markers for some time now. They are these awesome markers made for shading (they also have sketch markers). The blending done with these markers is so pretty. Unfortunately, they are not cheap so they have kind of hit the back burner of my craft supply list.
This is a great tutorial to show very basic use of the Copics. The Tranquil Waterfall tutorial provides step-by-step instructions for a detailed image. I am so impressed. The Copic site also has a section for tutorials. And here is a site with a huge roundup of Copic tutorials.
I most frequently see Copics being used for Manga (type of Japanese comic) art or by stampers that make cards. Although I found some really cute cards for this post, I generally see tons of cards with little people on them. Although the Copics work well for people (skin shading and what-not), I would love to see Copics used in other ways.