A couple of tools that are useful in creating visualizations.
First the Open Graph Viz Platform is freely available for Windows, Mac, & Linux at http://gephi.org/. This software is useful for creating a variety of undirected node-link diagrams (aka graphs, networks) and can handle datasets of up to 50,000 nodes and 1,000,000 edges.
The second is the OpenRefine tool for cleaning up data and is available at http://openrefine.org/. This is an open-source effort to extend and maintain the excellent and widely used Google Refine tool that has unfortunately ceased development. In addition to cleaning up messy data OpenRefine can also extending data through links to web services and databases. They’ve produced a great video showing off how useful OpenRefine/Google Refine can be
Lastly, if you want to get your hands dirty this post at the Online Journalism Blog will walk you through cleaning up some dirty data.