Class Zone - Features practice quizzes, practice tests, a problem of the week, and help with individual lessons or chapters. http://www.classzone.com/books/geometry/index.cfm
Online Conversion - Will convert to any unit you need. VERY helpful for homework problems, projects, etc. http://www.onlineconversion.com/
Prentice-Hall Geometry Book - a student help page with extra practice, challenging problems, and chapter outlines. From a different book than we use in class, but Geometry nonetheless. http://www.phschool.com/atschool/Mathematics/Geometry/Student_Area/GEO_S_BK_index.html
CoolMath.com is an interactive website with games and lessons for basic review of algebra and other math skills. This is very good for students who are looking for more practice, and also for students who want another explanation of some concepts that we have covered in class. http://www.coolmath.com