Free GIS for ecologists, biogeographers and evolutionary biologists
My colleague Neftalí Sillero and Pedro Tarroso have published recently a nice comparative review of different free and open source Geographic Information Systems (GIS) which can be useful to ecologists and evolutionary biologists willing to start using these tools or trying alternatives to proprietary software (mostly ArcGIS). Many freely available GIS (e.g. QuantumGIS, gvSIG, GRASS, DIVA-GIS) are mature enough to fulfill most needs of average users. gvSIG and QuantumGIS are probably the most complete. For occasional users I always recommend DIVA-GIS for its ease of use and focus on ecological and species distribution analyses. The review also includes useful information on free internet data sources for climatic, environmental and other types of data.
Nonetheless, most of the analyses typically included in specific GIS software can now be performed in R - easily, efficiently and for free. The recent addition of the raster package has brought many GIS capabilities that were still lacking in R. Now R can be used as a powerful GIS for both vectorial and raster data analysis and visualisation. The CRAN task view on spatial data analysis serves as a helpful introduction to the packages and types of analyses available. Furthermore, besides the package manuals there is quite a lot of information on the web, including e.g. a tutorial on species distribution modelling with R.