Dynamic mathematics that students can actually play with
Community Review for Math Open Reference
This website has an excellent section dedicated to geometric constructions. The number of constructions is just as impressive as the quality found in each one. You can find every construction mentioned in the Common Core State Standards for geometry, in addition to many more for your advanced learners. Each construction includes a step-by-step animated demonstration of the construction, a list of the steps for offline use, and a formal proof of the construction. And this is just the beginning. There is also a page on the site dedicated to the Common Core State Standards that hyperlinks each standard to related content. The creator is very active and always adding more valuable content.
I like the comprehensive coverage of the geometry curriculum on this site and the dynamic, interactive animations that illuminate otherwise abstract mathematical concepts. There are ads on the site (mostly educational), so be aware of this as your students access the content.
One additional comment: the site has been updated to be compatible with the iPad! This is exciting for me, since my students are using iPads.
How I Use It
I use this website in many ways. For constructions, I use the animations to demonstrate the steps to bisect an angle, construct a perpendicular bisector, etc, prior to having students perform the constructions. I then set the animated constructions to loop while the students perform the construction with their own compass and straightedge. This method is more engaging and easily understood than using a whiteboard compass, and students can refer to the looping animation if they forget a step.
I also use this site for its vast library of vocabulary definitions with interactive animations. I use this for both teacher led lessons introducing the vocabulary as well as student led inquiry into the vocabulary.