I had the chance to work with some amazing illustrators before. It's actually not very hard to find them, just go to the places where they usually hang out. For the kind of designers I'm looking for, that would be deviantart and to a lesser extend dribbble.
Finding designers and working with them are two separate problems though. They speak in a different language so communication can be an issue. Also I found the design crowd to be very opinionated (just like us developers).
Textual requirement specifications don't work so well, instead replace them with sketches and concept ideas, color palettes, mood boards and a lot of IM communication. Also try to keep the iterations short, ask them to show you the work in progress at least a few times a week. You may also try synchronous design sessions, as described here: http://taptaptap.com/blog/the-design-session
Finding designers and working with them are two separate problems though. They speak in a different language so communication can be an issue. Also I found the design crowd to be very opinionated (just like us developers).
Textual requirement specifications don't work so well, instead replace them with sketches and concept ideas, color palettes, mood boards and a lot of IM communication. Also try to keep the iterations short, ask them to show you the work in progress at least a few times a week. You may also try synchronous design sessions, as described here: http://taptaptap.com/blog/the-design-session