Here's a list that I know of:
Cliff Aberson
Red Badgro
Norman Bass
Jim Bedford
Dutch Bergman
Charles Berry
Joe Berry
Larry Bettencourt
Hugo Bezdek
Lyle Bigbee
George Brickley
Tom Brown
Garyland Buckeye
Bruce Caldwell
Ralph Capron
Jim Castiglia
Chuck Corgan
Paul Desjardien
D.J. Dozier
Chuck Dressen
Paddy Driscoll
Oscar Eckhardt
Steve Filipowicz
Bob Fitzke
Paul Florence
Walter French
Wally Gilbert
Norm Glockson
Frank Grube
Bruno Haas
Hinkey Haines
George Halas
Carroll Hardy
Drew Henson
Bo Jackson
Vic Janowicz
Rex Johnston
Brian Jordan
Matt Kinzer
Bert Kuczynski
Pete Laydon
Jim Levey
Dean Look
Wally Macphee
Howard Maple
Walt Masters
John Mohardt
Greasy Neale
Ernie Nevers
Ossie Orwoll
Ace Parker
Jack Perrin
Al Pierotti
Pid Purdy
Dick Reichle
Deion Sanders
Johnny Scalzi
John Singleton
Red Smith
Hank Soar
Evar Swanson
Jim Thorpe
Andy Tomasic
Frank Umont
Luke Urban
Joe Vance
Ernie Vick
Tom Whelan ( First to ever do it)
Mike Wilson
Hoge Workman
Ab Wright
Tom Yewcic
Russ Young
Joe Zapustas
Here's another source:
Chat with our AI personalities
I'm sure there are probably more, but two players that come to mind are
Bo Jackson - played for the Chicago White Sox and the (L.A.) Raiders at the same time.
Dion Sanders - Played for the Altanta Falcons and Atlanta Braves at the same time.
Jim Thorpe. He played in MLB between 1913-1919 and in the NFL between 1920-1928.