R is free to download and use, and all the codes are open. At the same time, users can easily add their own programs (once they are familiar with statistics and programming).
SAS is a powerful statistical-analysis and data-management system for complex data sets. It is especially strong in analysis of variance (ANOVA), the general linear model, and their extensions.
SPSS performs statistical analysis on quantitative data. The graphical user interface makes statistics analysis easier, including most complex models.
Stata is a command-based statistical package that offers a lot flexibility for data analysis. The program language keeps a simple structure, so is easy to learn, allowing users to focus on the statistical modeling.
Excel is good is for the simplest descriptive statistics, or for more than a very few columns. It is easy to use for basic data analysis, and is much more convenient for data entry and shape manipulating.
NVivo is a qualitative data analysis package. It helps researchers organize and analyze complex non-numerical or unstructured data, both text and multimedia. The software allows users to classify, sort, and arrange thousands of pieces of information. It also accommodates a wide range of research methods. It supports documents in many languages.
Quantum GIS (QGIS) is open source GIS software, available for both Windows and Mac OS. This software is free and comes with surprisingly powerful and useful tools.