Haha ... I have the opposite problem: no lack of ideas, but a lack of my ability to execute (on my own). I think it's because I am a customer facing (marketing/bizdev/sales) person at heart though my forte is product (management). Anyway, my ideas all come from customer interaction. And I have heard it from many others: just pick something as long as it gives you an excuse to interact with real customers. This is a bit easier in the enterprise market where you can engage with real customers. Partnering with somebody who has credibility with those guys and can get you meetings also helps.