Cabri


Cabri 3D v2.1.1 evaluation version downloadable from http://www.cabri.com/v2/pages/en/downloads_cabri3d.php
Cabri II Plus evaluation version downloadable from http://www.cabri.com/v2/pages/en/downloads_cabri2plus.php

HandyGraph


Fully functional evaluation downloadable from http://www.handygraph.com/download.php

GeoGebra


Full versions of GeoGebra:
GeoGebra WebStart: http://www.geogebra.org/webstart
GeoGebra Download: http://www.geogebra.org/download

ILNumerics


Math Library for C#/.NET that features a Scene Graph API for 2D and 3D Visualizations. The Community Edition (GPL 3) is free: http://ilnumerics.net/download-ilnumerics.html

Cinderella


Trial version downloadable from http://cinderella.de/tiki-index.php?page=Download+Cinderella.2

Maple 11


No trial version available.

Mathematica


Request a trial version using the form at http://www.wolfram.com/products/mathematica/experience/request.cgi

TI-nSpire CAS


Download the trial at http://education.ti.com/educationportal/appsdelivery/download/download_eula.jsp?cid=us&displayMode=F&applicationid=6667&contentpaneid=7

Autograph


Trial software at http://www.autograph-math.com/downloads/download_30daytrial.shtml

The Geometer's Sketchpad


Instructor's Evaluation Edition available by filling out the form at http://www.dynamicgeometry.com/instructor_resources/evaluation_edition/index.php

Spherical Easel


Can be downloaded from http://merganser.math.gvsu.edu/easel/