Brief collection of strategies that you can use to generate new ideas for startups:
Repurpose
Take a service or approach applied to one market, and apply it to another.
Examples: Chill (Turntable.fm), Yammer (social networks for businesses)
Digitize
Take content or functionality that exists only in a legacy form and put it online or in an app.
Examples: Dr. Chrono (medical records), Google Books
Automate
Take a task that seems tedious and currently requires humans and automate it away.
Examples: Google (search rankings), EffectCheck (emotional impact analysis)
Unify
Create a common platform that ties together proprietary solutions or providers.
Examples: Twilio (abstracts away carrier-specific APIs), Greplin (single search engine for lots of services)
Componentize
Take a piece of functionality that people currently implement themselves and make it a reusable component.
Examples: Apigee (APIs), Get Satisfaction (support forums)
Connect
Transform a situation where people are isolated or lonely by connecting them in a novel way.
Examples: Facebook, Meetup, LetsLunch
Catalyze
Encourage people in a community to generate data that would otherwise be less structured or available.
Examples: StackOverflow (programming Q/A), reddit (social news), Curvio (IMDB for products and apparel)