Paul Graham wrote a post about ideas he'd like to see: http://ycombinator.com/ideas.html.
My advice is to get out and about in your community, and find real problems. Then make something which solves (part of) that. Even better if it's a problem for you. It can be hard to stick with a project if you aren't using it yourself.
Here's another great blog post, with a checklist to go through when an idea starts to form: http://rowansimpson.com/2011/10/23/from-idea-to-impact/