I’ve been referred to some really, really awesome datasets.  I wish I had known about these while taking data-analysis classes in college.

• theinfo.org
• infochimps.org
• PoliParse

My personal favorite is the Enron emails of 150 employees, mostly executives.  Included are their names, their sent items, inboxes, notes, etc.  WOW would I have a blast hacking away at this for hours.