I love Geogebra! For years I have been using Autograph and Geometer’s Sketchpad with great success but Geogebra is in a class by itself. The best part? Its FREE! When you are running a 1:1 program, for mathematics this is gold.
In the spirit of Dan Meyer and WCYDWT (what can you do with this), I had students use their mobile phones to take pictures of a water stream from a hose (we are studying quadratics). Students imported their photos into Geogebra and then modeled the water stream by manipulating sliders representing the parameters of a general quadratic function. The best part of this activity was then getting the students to ask questions about what they would like to know. Some were interested in how fast the water was coming out of the hose, while others were interested in how high above the ground the water reached. They became responsible for answering these questions and I must say, they did a pretty good job.
I am finding myself using Geogebra extensively in both SL and HL classes particularly with the functions/polynomials unit but I have only scratched the surface of what Geogebra is capable of.
I strongly urge you all to give it a try. There are a great deal of resources available for support and teaching and there is an extensive collaborative wiki where teachers can upload and download their favourite activities. Have fun!