From the dawn of mankind, ideas have pushed the boundaries of reality and expanded our knowledge and capabilities. The first person who realized how fire can be used to cook food, or the first person to invent the wheel had a huge challenge in reaping the rewards of their invention. The reduction to practice may have been simple, but the dissemination and protection of ideas had to wait a few thousand years to the era of patents and writing.
Today, inventors and idea originators have a whole system to protect their ideas, but the reduction to practice, and commercialization are often a daunting task.
The simple case is an idea which can become a company. In this case, the idea originator either forms a company, builds a team and raises money to make the idea happen or he should find an entrepreneur who has the drive to create a company around the idea.
Other ideas are challenged to become companies. These ideas typically exist within an ecosystem of constraints, or within established markets (e.g. toys, food etc) which require extensive capital to bring products to market. In these cases while the option of forming a company is possible alternatives such as open innovation are attractive. the following is a partial list of sites which offer challenges and are seeking ideas. These sites present a lower effort route than forming a company towards commercialization of ideas.
Quirky is a site mostly aimed at gadgets
NineSigma typically provides technical problems from large companies
Innocentive also offers less technical challenges
Kaggle is geared towards the data scientist
Intellectual Ventures focuses on building long term relationships with its inventors