I'll definitely be making some skins as soon as I pick up my DS.
Thegame07, I like your skins, but I reckon you could easily do something like that Vincent one you posted.
If I can make a suggestion: I noticed most of yours look very similar in the top and bottom screens. They clash a little. I think it looks better if you make the top screen as something detailed like a character, but keep the bottom screen as some kind of simple pattern or landscape to complement the top.
Like if you're doing a Solid Snake theme just do a close up of his face, or him crouching against a wall for the top, then for the bottom just his camoflauge, an empty hallway, or close up of dog tags.
Not sure.... I suck at photoshop actually. Just thinking out loud.
Edit: That Darth Vader one rules. It'll go well with my black DS.