Video Game Concept Artist (2d)

We are looking for a concept artist to help us take our 2d puzzle/platform prototype to the next level and help establish the art direction for the game. We have a functional prototype with established mechanics and we would like an artist to help us find the style.

Playable Prototype (requires Unity Web Plugin): http://www.ludumdare.com/compo/ludum-dare-28/?action=preview&uid=25189

You would be responsible for:
Mocking up 1-2 sample game screens that simulate near final quality.

Create thumbnail variations for some of the different game elements (player avatar, switches, lights ect.)

Deliver art content in a way that can be easily reused in-game (ie elements broken up on different layers)