I have this hankering to get started on a web app (Not really for YCombinator, but more because I have the time and really want to spend a chunk of time coding).
My problem is I have yet to find a web app that's lacking for my own needs. Tons of news sites, tons of tech sites for questions. This brings up a problem with trying to find a project to dig into.
So, what web app do you want to see happen? What niche, or need do you have that is not currently solved? The bigger the better, and the more interactive the better (I really miss doing heavy JS, so the more interaction needed, the better). Finance is not really my area of expertise, but anything outside that I can consider and think if it's feasible.