[ronyeh]

Behance looks good. Thanks for the tip!

I'd rather avoid generic contracting/freelance sites, as I feel like the quality would be "all over the map" as you say.

I'd prefer looking for artist communities, especially if they have forums that talk about iOS/Android game art.

[NateLipscomb]

No problem. Although I think Behance is probably better for your purposes, you might also want to check out DeviantArt (deviantart.com). It's another pretty big artist community, although I'm not sure how many game artists are on it.