Partial list of Wild Wild West actors appearing on Star Trek (TOS):
Dick Cangey - Otto (Space Seed)
Bob Herron - J. Hunter stunt double
Michael Dunn - Dr. Loveless
Chuck O’Brien - Shatner stunt double
William Schallert
Robert Phillips - The Cage
Arthur Batanides - D’Amato
Walter Edmonton - Balok voice
Anthony Caruso - Oxmyx
Theodore Marcuse - Korob
Paul Comi - Stiles
Gregg Palmer - Spectre of the Gun
Morgan Farley - Archons/Omega Glory
Jon Lormer - Archons
Sebastian Tom - Shore Leave (Warrior)
Jack Perkins - Bread & Circuses
Alfred Ryder - Crater (Man Trap)
Jason Evers - Rael (Wink of an Eye)
Jeff Corey - Cloud Minders
Kathie Browne (Mrs. Darren McGavin) - Wink of an Eye
Harry Townes - Archons
John Hoyt - Dr. Boyce
Maggie Thrett - Ruth (Mudd’s Women)
Sherry Jackson - Andrea
Paul Fix - Dr. Piper
Perry Lopez - Rodriguez (Shore Leave)
Joseph Ruskin - Galt
Leslie Parrish - Carolyn
Vince Howard - Crewman (Man Trap)
Marj Dusay - Spock’s Brain
Byron Morrow - Amok Time
Bill Zuckert - Specter of the Gun
Elisha Cook - Cogley
Judi Shervan - Wolf in the Fold
Chuck Courtney - Patterns of Force
Billy Curtis - Journey to Babel
(Either I recognized the face, the voice or the name in the credits)
Many more to come.