A new "Big Data" resource of tax material has recently been made available. On October 30, Public.Resource.Org made available 10 years' worth -- nearly 6.5 million -- Exempt Organization Form 990 returns filed by exempt organizations and private foundations as well as unrelated business income (UBIT) returns filed by these organizations. The data set contains returns from January 2002 through September 2012, and will be updated monthly.
At this time, these returns are only available in pdf format, but Public.Resource.Org plan to extract the underlying data from these returns to make them more amenable for data analysis.
These records and more information about the data set are available at https://bulk.resource.org/irs.gov/eo/readme.html.