It's called crowdsourcing and I haven't seen it really work because ideas are a dime a dozen. Create. Don't think about it.
("Yet Another Ad Network" doesn't capture my imagination)
I run a business. I've had ideas, and implemented them. I have ideas for future stuff.
In both cases, the ideas are hard to separate from me. I know the market, I know the users, I know what I can create, I know enough relevant tech.
I could give the ideas to another domain expert, and they could probably implement them. Though they'd have their own take on things. That would change things. Some for the good, some for the better.
Obviously, you can get ideas from external sources. But they'll be more powerful if they're based on your own experience or readings, so that you can bring everything to bear.
To be creative, you have to just create. Just find something small and work on that if you need a place to start.
One of my favorite projects was a (not illegal) archival site building off a private p2p tracker php app and writing a custom software that would automatically download and virus scan any uploaded torrents, and then approve the listing with the virus scan results.
If anything fishy had ever popped up, the plan was to remove it later. My partner and I were really the only ones who uploaded anything tho :P