If the dataset comes from the Gov't (e.g., Freedom of Info Act), one might argue that its public domain data. If its public domain, then slapping a license on it doesn't change anything.

If its not public domain, and you want people to use it fairly freely, Apache seems like a good license.

Disclaimer: i haven't thought about this very carefully before posting. Could be wrong.

One thing I do know is that @copiesofcopies is a former EFF guy that knows open source licensing. Ask him!