Last week I posted a short tutorial on how to merge datasets using R. R is a free and open-source statistical computing software and programming language (get R here). The only downside is a steeper learning curve because the documentation is sparse and often difficult to understand at first. Once you start using it, you'll realize it can do anything SPSS, SAS, and Stata can do, and its graphing capabilities are light years ahead of everything else. Lately it's use is becoming more mainstream, gaining popularity in the life sciences among other fields, and knowing how to use R is a marketable skill to have on a job hunt.
If you've used R at least a few times before then this printable reference card is really handy for remembering which functions do what and how to use them. If you've never used R before, there are several online resources to teach you the basics of R, and a free book (PDF) written specifically for people who have used SPSS or SAS before and now want to learn R. Also, check back here in the future for more R tutorials or examples.
R Reference Card (PDF) via Rpad.org