His Nobel lecture is highly recommended reading for my ECON110 class in the first week, and underpins a lot of the work we do in that class.
The University of Chicago website has a wonderful obituary, full of tributes from his colleagues and friends. I especially like this quote from Kevin Murphy:
Gary was an inspiration to several generations of Chicago students - instilling in them the love for economics that he lived and breathed.Economics teachers and university researchers should all aspire to this. The world of economics has lost one of its greatest contributors, and we are all a little poorer for that.
You can read more about Gary Becker and his contributions to economics here [HT: Greg Mankiw]. Marginal Revolution has links to "Some neglected Gary Becker open access pieces", which are well worth a read too.