The Buck Institute website, bie.org, is an excellent resource for project-based math education. Other sites, such as ct4me.net and emergentmath.com also offer project-based education resources for mathematics.
The Buck Institute is an international leader in the field of project-based learning, and their website offers a large selection of projects to choose from. Emergentmath.com offers a full suite of K-12 project-based learning curricula for mathematics, including advanced mathematics courses up to algebra 2. Alternatively, ct4me.com is a K-12 oriented site that allows you to customize math projects to fit the needs of any student.
All of these sites also offer a wealth of information on project-based learning theory and teaching methods.