A wealth of free online resources can assist teachers in finding strategies for incorporating new teaching ideas into their classrooms. Here are some great possibilities:
The Center for Industrial Mathematics and Statistics, offers a collection of industrial math projects aimed at high school students. The purpose of these projects is to incorporate mathematical principles with ways students might use math in the world of work.

Industrial projects combine math with careers.
Teachers have a wide range of options addressing statistics, calculus; projects can also be selected by career field. Career fields covered include communications, education, energy and finance.

Projects can be searched by math skill or industry.
The American Mathematical Society’s site, also includes a page with research projects for high school students. The site was born out of a common student struggle to find appropriate research topics.

The American Mathematical Society’s Projects page.
While the site does not list specific projects, it does link to a variety of resources teachers can use to help their students find and develop ideas for research projects. Selecting an appropriate topic and narrowing it down into a manageable project is often a challenge for both teachers and students.
One of the site’s suggestions is
Plus Magazine, an internet publication which emphasizes the many real-world applications for mathematics. Though the site is not intended to provide ready-to-use projects, it does feature the latest mathematical research and has a lot of high-quality content, making an excellent source of ideas.

Plus Magazine is an up-to-date resource.
Cornell University’s mathematics department has created the
Math Explorer’s Club, with support from the National Science Foundation.

The Math Explorer’s Club addresses projects in most areas of math.
Unlike the two prior sites, the Math Explorer’s Club includes middle-level appropriate projects. There are approximately forty projects organized into different branches of mathematics. The materials are aimed primarily at teachers, who can modify the materials to make them more appropriate based on the students’ abilities. Most projects are accompanied by lessons, making them appropriate for whole-class exploration.

Auction theory provides a great hands-on idea.
The Math Forum @Drexel, features Ask Dr. Math, which uses a star to indicate projects which generate unique or interesting answers. The collection includes about forty projects.

Dr. Math features a lot of great content.
Nearly all the projects date back to the late nineties and consist primarily of project-related questions from students. However, teachers may find that much of the content is relevant and may help with the development of project ideas.

The site uses a Q&A format.
Finally,
GrandpaMath.net, includes a list originally created by Afton H. Clayford at the University of British Columbia.

GrandpaMath features a list of ideas .
The list, which includes 60 possibilities, has situations which require additional research and development. In addition to the project possibilities, there is also a list of books teachers can use to locate additional ideas.
Teachers may still need to do some additional preparation to implement many of these projects. However, the above sites provide solid ideas to help teachers and students develop challenging, worthwhile projects.