I first saw Mr. Zimbalist's work on The F.B.I. television series, which my family watched every Sunday evening when I was little (and which my dad always called The F.B.I. Story, actually the title of a James Stewart film).
When I finally discovered Jack Kelly and Maverick many years later, I was delighted to watch Mr. Zimbalist guest star several times on the series as the suave con-artist Dandy Jim Buckley.
JK and EZJ also worked together in the 1961 Warner Bros. feature film A Fever in the Blood, as shown in this still:
Great news: A Fever in the Blood will air this Wednesday, May 14, on Turner Classic Movies in the US at 4:00 pm ET (check your local cable/satellite guide for correct time/channel).
More info about this rarely seen classic can be found in this 2009 TDS post. (I guess TCM heard me! ;->)
I'm thankful that Efrem Zimbalist Jr. left a long legacy of performances for us to enjoy. Rest in peace, sir.
*******************************
UPDATE (5/23/14): A Fever in the Blood has just been released on DVD! It's available from WB Shop.com for $18.95 and $2.50 standard shipping (in the US only at this time).