Occasionally in the casts, M&M will refer to a cast as a 'Hall of Fame' cast, stressing that they think its an important one.
In iTunes, I've created my own HOF playlist where I put some of the casts I think are HOF worthy. These aren't the 'Basics' (i have that playlist too) but are ones I like to listen to every few months to keep my edge and remind me of things (Organization finance basics, Trinity 1-4, DISC summary, etc).
Interested to what other forum member (and M&M) consider 'HOF' casts ....

and hidden gems
A few of my favorites:
Managing during mergers and acquisitions - useful for ANY organizational changes.
How to prewire a meeting. Don't make a proposal without listening to this cast.
Managing your Boss - communicate effectively!
Late Stage Coaching - it's about making everyone successful
Time Management - what are your priorities?
Juggling Koan - great reminder
and one last one, useful as we approach the holiday season:
Time to Party!
John Hack
I'll add a few others...
The 4 part series on performance review preparation
How to Create a Simple Behavioral Interview Question
Interview Results Capture Meeting
How to be Persuasive in a Presentation
Write More Effectively