I've been using GSP (Geometer's Sketchpad) for some time. There's a lot to like about it, but I find more and more shortcomings. I wish I could enter a vector in an input line or "algebra window," for instance, and see an arrow appear on the screen. I also wish I could work in 3D without quite so much hassle (GSP was never intended for that, though there are user packages).
Sometimes I think Geogrebra is better, not to mention cheaper. In version 5 Beta, you can open a 3D window. Still in Beta, limited features, but still a lot easier to use than GSP.
I've heard of Cabri, a European product, but I hesitate to shell out $200 without learning more about it.
I wonder if anybody has comments or suggestions.