I was discussing this resource in class a couple of weeks ago, so I thought I would share it. The website summarizes the study nicely:
"The 2003 National Assessment of Adult Literacy is a nationally representative assessment of English literacy among American adults age 16 and older. Sponsored by the National Center for Education Statistics (NCES), NAAL is the nation's most comprehensive measure of adult literacy since the 1992 National Adult Literacy Survey (NALS)."
I really enjoyed reading about the complexities of assessing literacy and establishing research methods in their discussion of "Indirect County and State Estimates of the Percentage of Adults at the Lowest Literacy Level for 1992 and 2003" (http://nces.ed.gov/pubsearch/pubsinfo.asp?pubid=2009482).
But the part that I enjoyed playing with was the model that this document describes. It allows comparisons and estimates of low literacy rates by state and county. Basically you can compare two states or counties and it will show you the proportion of the population below a basic literacy rate (with the standard deviations of the stats). It's just a nice interface with which to browse the statistics.
See http://nces.ed.gov/naal/estimates/ for more info and to play with their model.