Do a "Ask HN:" type post at Hacker News. Those guys are usually pretty good about giving some comments on new ideas. Sometimes a bit cynical. But overall a good community.
Also, you might want to read stuff coming from this guy recently:
He's been writing about his real world experiences doing customer development. Basically the bouncing of ideas off of the people who might the customer of that idea.
I also love the story Keith Schacht, the CEO of Crafted Fun, has about testing an idea. He had some idea for an application to help bar managers. All he did was draw some stuff up an paper, walked over to 3 bars in his neighborhood, and asked to talk to the manager. He talked with a few folks and figured out some great stuff that helped him avoid working on the idea, and he moved on to the next idea.
His main point is, you can definitely craft some kind of minimal idea on paper to show off. But then next you need to get off your butt, even virtually, and go find people. Lots of people hate sales calls, but those same people like talking about new ideas. So don't sell, just try and find people to talk with who could look like your customers.
And of course, you probably want to read Steve Blank.