I think you pretty much find everything on deviantart, from brushes to tutorials. But, for those in need;
[Wall Tuts] Desktop Zero Nigen Inamations Mixed Media Angel Wings
*note* these are only tips, and help on the little details, making a wall takes a lot of creativity, this only shows you how to create whatever you think of.
[Anime Tuts] Vectoring Tekuteku [Web Design] Photoshop to Dreamweaver Framing your Content [Dark Art] Onus Art [Space Tuts] Everything on Space Scenes
those are most of the stuff I've used when creating walls, and whatever it is I do, a lot of these aren't meant for biginners. If you need some help feel free to contact me.