One podcast that I used to listen to regularly, I haven't for a while as I just don't have the time, is Mysterious Universe by a couple of guys in Sydney. Technically it's very good and they have spent a lot of money on getting a proper room setup and have decent mics and equipment. The content can be really interesting as well.

The way the podcast is mixed and put together is incredibly good, with great research etc.

Apart from that one I really don't listen to any others. I should get back into podcasts again!

I don't listen to many, but the ones I enjoy are WTF with Marc Maron and Doug Loves Movies. Both can be really funny, and Marc Maron does really good inspiring interviews (check the interviews with Conan O'brien, and Ray Ramano).

Both I think are recorded well enough, but not alot seems to be put into the post cleaning things up. DLM tends to have alot of low end mic handling noise that bothers me when I listen to it on some of my systems.

I record The Panel (with Stephen Edwards). It's been interesting to record, and I've evolved how I record it each episode. Getting better results each time. I also spend time compressing and automating a few parts when people talk over each other. I'm most pleased with the latest, Episode 4. Just finished it up and should be posted in a few days.

Soundworks Collections (non video) sound good too.

I'm not a regular podcast listener but I like to follow The Game Audio Podcast and Soundworks Collection's stuff more than others, and the best sounding ones I think I'd say Dolbycast and Shure cast.

Radiolab from WNYC is really good...from the way the hosts sound right across content, music, sound design.

For both quality and content I am fairly addicted to (1) This week in Tech with Leo Laporte and his panels and (2) the No Agenda Show with Adam Curry (mtv) and John C Dvorak. Both shows are heavily researched and the quality is better than 99.9% of everything else out there

I sometimes listen to podcasts from Resonance FM. It's an arts based radio station in London.

Freakonomics is great. Very interesting content. I also like Radiolab.

Top Score with Emily Reese is probably the best quality podcast I listen to, most of the others are generally just talk based and are created with "quickness" and content.

Quite a few of them I listen to aren't even mixed, they are just edited... which makes some sense when they are churning out an hour long podcast a week as a hobby and I'm usually just going to listen to it in my car.

TWiT, referenced above, is a very well-produced and good sounding podcast.

For good sound design, check out Cayenne Chris Conroy's podcast at TekDiff.com
It alternates between a sketch comedy show (called Tekdiff and a sequential narrative show called The Account). Both are well designed, although sometimes the mastering is a bit off.