Michael Feldman's Whad'ya Know?, I used to listen to this when I drove back from my parents house to the Cities:)
A Prairie Home Companion, a staple when I was growing up.
This American Life, which I always used to listen to when driving from Minneapolis to Iowa City to visit my family.
Car Talk, does it get any better than Click & Clack?
I also like Wait, Wait Don't Tell Me, but only the week it airs. Plus I like Mountain Stage, and of course All Things Considered. I am such a nerd.