Though not quite what you're looking for, StyleForum (mentioned in another comment) has a "What are you Wearing Right Now" thread in the Men's Clothing section... you can actually try out different combos and receive (mostly) constructive feedback.

I believe that hn's vaksel runs a site close to that - http://styleguidance.com/

Although it does seem geared slightly more at women than men, I think it gets pretty close to what you're looking for. Perhaps vaksel can work with you to round out the rough spots.