I recall Jolene Blalock in some episodes, and Robert Picardo, too. I can't recall anyone else off the top of my head, but there are bound to be a few more.
In the Line of Duty
had interesting ramifications.
I forget when they started the intense DVD commentaries (For most of the series, the directors, producers, actors, or others would provide a running commentary for the entire
episode. All of it was interesting, like an advanced TV production/directing/acting class, and much of it was hilarious, such as a long passionate debate on the merits of Dixie Cream donuts versus Tim Horton's.
The director's series (seperate from the voice-commentary) is posted on Youtube, but it would be thick with spoilers.