Looking for feedback on a business idea?
There are any number of forums on the internet which allow you to post your idea and have it evaluated by others. Depending on the individual site, the posting may be free, or for a nominal fee.
Every site is a little bit different--some gear themselves towards getting ideas funding while others take a broader approach to the concept of community and attempt to include as many aspects of entrepreneurship as possible.
You decide what qualifies as a good site. If you feel comfortable with what you find, then post on the site for feedback. If you don't like what you see, then don't post.
Also, adapt your idea to the forum. Post a full business plan in the forum allows form. Post an executive summary if that's what the community supports. You will go wrong only if you don't follow the spoken and unspoken rules of the community. Don't be afraid to make mistakes by learning--everyone has to start somewhere.
Find the community that will best support your needs above all else.