Well, the first book-related podcast that comes to mind is Books on the Nightstand. Ann Kingman and Michael Kindness link to their weekly podcast in their blog by the same name. Each week they discuss books they love, books they can't wait to read, books by genre, and whatever else they think their listeners might be interested in. I always enjoy listening to their podcasts, but I can't listen to them in the car because I always end up needing to write down the titles to at least two or three books, and I don't want to try to do that while I'm driving! I find this to be a good end-of-day podcast-you can sit in the dark and listen to a couple of friends talk about books, add a couple of titles to your ever-growing TBR list, and then go to bed.
My other favorite podcast has nothing to do with books at all. It's Car Talk, and it's hosted by Click and Clack, the Tappet brothers, a.k.a. Ray and Tom Magliozzi, a couple of MIT-educated auto mechanics who take calls about people's cars. I know this doesn't sound very exciting but it's hilarious! Click around on their web site a little bit and you get a feel for the self-deprecating wackiness that Tom and Ray exude on every show. It's impossible to listen to them and not be in a good mood by the end of it. They clearly have a great time doing what they're doing, and it comes across in every podcast. You don't have to be a car enthusiast to enjoy this show, heck, you don't even have to own a car! This one is good for listening to in the car though!