In descending order of favorite-ness:
Gay Pimpin' with Jonny McGovern It's very, very gay, so I don't expect anyone else to like it. They talk about wiener an awful lot, and it's incredibly infantile and inside-joke-y, ie. perfect for me.
WNYC's Radio Lab Most everyone who listens to one episode falls immediately in love with it. It's a look at very simple things, like sleep, from a scientific perspective. But done in a really engaging manner. Not your father's Discovery channel.
KCRW's The Business A look at Hollywood from the business side. I don't like Kim Masters, the host, as much as I did her predecessor. However I still like it. I find the business side of Hollywood more interesting than the artistic side sometimes.
KCRW's Design and Architecture It's only 30 minutes long and it only comes out once a month. Even though it's called "Design and Architecture" it mostly concerns architecture. It's focused on southern California. I like that because it's about stuff that I don't know about in Dallas.
On the Media We already talked about this in another thread.
Studio 360 with Kurt Andersen Andersen is just a wonderful, wonderful interviewer and host. Sometimes the subjects are outside of my interests, but I listen anyway.
This American Life Enough has been said about it.
Onion News Network Ditto.
PRI: The Sound of Young America Jesse Thorne is another great host, and he fits the public-radio mold to a T. Because his interests trend younger than Andersen or Terry Gross, he takes a "younger" approach. He's more self-aware, and he doesn't mind inserting himself into guest banter. Sometimes that gets on my nerves, but other times it doesn't.
KCRW's The Treatment I listen faithfully, and sometimes I don't know why. I'm ambivalent about the show. A lot of the time I actively dislike Elvis Mitchell. Other times I love the answers he gets from his guests.