There are a variety of tools available--many of them open source--to help you turn your data into a visualization, or simply to explore other people's visualizations.
This 4 minutes video provides a great overview of Visual Understanding Environment (VUE). VUE is an open source project based at Tufts University,. A great software for turning your data into attractive visualization. For detail consult User Guide
If you wish to build a visualization from the ground up, you can use the Java programming language to build an applet, or software such as Adobe Flash. Below are some resources that may help you develop a data visualization with a programming or scripting language.
These are just some of the many tools and projects available on the web.