What medical school courses are actually beneficial to a practicing physician, specifically a psychiatrist?

It's not the individual pieces of information that matter, but the education as a whole.

What I learned in 1985 may or may not be applicable today, but I have a good foundation of knowledge upon which to build when new information becomes available.

I will never have to regurgitate each step of the Krebs cycle again (God willing!), but I may need to understand how a condition or drug affects it.  A psychiatrist may not need to know the finer points of renal physiology, but he/she WILL have patients with kidney problems, and will need to understand the impact of psychotropic medications on renal function, and vice versa.

I've probably forgotten more than most people ever learn, but when I need to understand something new, or remind myself just how or why something works, I can do it.

You've got to learn it all.