Like the last suggestion - but that turns it more into a competition style site really.  Try DPChallenge.com for some good honest (and blind) feedback in a challenge scenario.

One of the things is that a lot of people put watermarks so the pictures wont be truly anonymous - i can tell a couple of photographers styles on here too so i wouldnt have too many problems picking them out even without watermarks.

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography