Idea, Innovation and Invention Contests - Idea Connection - This is a big list of competitions in a variety of fields. Most of them are innovation contests in one way or another. Architecture and related fields are heavily represented. A lot of other areas are included, too.
A few sample subjects: web design, water use, United Nations goals, prison design, bathroom and kitchen innovation, "liquid landscapes", Intellivision programming, global warming, digital imaging, sustainable cities, various art fields, furniture, "mobile floating architecture", intelligent transportation, fire science, and designing planned museums and libraries.