Google Earth lets you fly anywhere on Earth to view satellite imagery, maps, terrain, 3D buildings and even explore galaxies in the Sky. You can explore rich geographical content, save your toured places and share with others. (from Google Earth Page)
ArcGIS Explorer delivers an easy-to-use way to view and share information geographically. Download ArcGIS Explorer and start using it to unlock the power of geography and geographic information. ArcGIS Explorer is free and freely distributable, making it a great way to share your maps with others. (from ESRI site)
World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data, World Wind lets you experience Earth terrain in visually rich 3D, just as if you were really there.
Virtually visit any place in the world. Look across the Andes, into the Grand Canyon, over the Alps, or along the African Sahara. (from Nasa site)
ArcGIS is a powerful tool for working with spatial data and it is the industry standard for researchers and professionals working with GIS. Washington University in St. Louis currently has a campus wide site license for the ESRI ArcGIS Software suite, making it available to all students, faculty, and staff for research and teaching purposes. See this guide for licensing and installation instructions. You can also access ArcGIS desktop in most computer labs on campus, as well as in the dedicated GIS Teaching Lab.
Hawth's Analysis Tools is an extension for ESRI's ArcGIS (specifically ArcMap). It is designed to perform spatial analysis and functions that cannot be conveniently accomplished with out-of-the-box ArcGIS.
Most of these analysis tools have been written within the context of the ecological applications I am involved in (movement analysis, resource selection, predator prey interactions and trophic cascades). However, they have been created in such a way as to be as broadly applicable as possible such that I hope people from many disciplines will find use in this set of tools.
There are three types of tools in this kit. First, there are simple tools that automate mundane tasks (e.g. deleting many fields at once from a table). These will likely be useful to anyone.
Second, there are tools that are designed to be part of an analysis workflow. For instance, random point (or stratified random point) generation, minimum convex polygon delineation, summarizing raster layers in various ways, etc. These too are likely to be useful to many people.
Finally, there are tools that target specific, ecology related analyses (for instance, various movement model applications). These will likely only be of interest to ecologists.
Specific detail of the tools can be found on the Tools page.
Hawth's Tools is FREE. You are free to distribute it and install it anywhere you choose. As there are continual updates and additions to the tools, it is recommended that you check this website from time to time for more recent versions.
I am always happy to hear constructive suggestions and comments about these tools.