At Ideasicle, we come up with lots of different kinds of ideas - names, tag lines, promotions, app functionality, you name it. But our favorite kind of idea isn't a "kind" at all. It's so blue sky that's what we call it - "Blue Sky Ideas" - and it's when a client asks "How are we going to launch this?"
With Blue Sky projects, the client does not dictate what kind of idea, just illustrates the problem. Sure, we ask for any parameters around the project like budget and timing, but that's really it. Anything goes.