I haven't listened to any since I no longer spend my work day in the car, but if you're a dork like me, you might enjoy:

Tales from the Magic Tavern: A man from Chicago gets sucked into a portal and finds himself in a fantasy world of wizards, Orcs, and a nasty little shapeshifting badger. There is a structured plot line, but all dialogue is improvised.

Hey Riddle Riddle: That nasty little badger from Magic Tavern started his own podcast that focuses on riddles. They ask each other riddles and the listener can try to solve them as the hosts figure it out. Also, full of silly improv scenes between riddles

Dungeons & Daddies: Follows a D&D game in which a group of dads and their sons are transported from our world into the Forgotten Realms. The Dads must use their newfound D&D powers to save their children. Very funny, AMAZING STORY. The DM does a great job, and was a lead writer for Borderlands 2, if that means anything to you.

Get Played: Originally they only covered terrible or bizarre video games, but expanded to weird/ mind bending games. They introduced me to some really good underrated Indy games.

Here's the Situation: Two Improvisors that present each other with scenarios and they just give their honest opinion on it. For example, of you could only eat one candy for the rest of your life, what would it be? What if there was an organized draft (like in sports) and only one person could claim each candy? How much do you think you could sell an actual magic item for on eBay? They ended it years ago, but it was fun to bring the situations back to my family and see what they thought.