Omnibus with raconteur John Roderick, and quiz kid Ken Jennings is one of my favorite podcasts. Light-hearted,odd history.
The ease at which John and Merlin weave between interesting subjects and cool stories from mostly-John's bonkers life is really something to behold.
EDIT: Also, John has another podcast with Dan Benjamin, "Road Work," that is a lot more focused on how John's peculiar mind works. It is very good too!
Don't forget about "Friendly Fire", the war movie podcast. His love of history comes through in that almost as much as in "Omnibus."