((FYI - I'm really bored and have insomnia. That's the only reason why I did this, lol))

Well I see the actors that play Hammond, Carter & Frasier from SG1 right off the bat were both in X-Files (I knew I recognized the guy that plays Hammond from somewhere).

This is what I found. (Everyone except for Amanda Tapping and Teryl Roth who were only in X-files for one episode - everyone else on the list are actors that were in each show at least twice, whether for the same character or different characters):

William B Davis (Smoking Man / Damaris)

Steven Williams (Mr. X / General Vidrine)

Bill Dow (Dr. Charles Burks / Dr. Bill Lee)

Doug Abrahams (Agent / Ori Prior)

Adam Baldwin (Knowle Rohrer / Colonel Dave Dixon)

Steve Makaj (Misc Characters / Colonel Makepeace)

Peter Kelamis (Misc Characters / Coyle Boron & Dr. Langham)

Mitchell Kosterman (Misc Characters / Colonel Tom Rundell)

Don Thompson (Misc Characters / Property Master)

Roger R. Cross (Misc Characters / Captain Conner)

Gillian Barber (Penny Northern / Ambassador Dreylock)

Robin Mossley (Dr. Kingsley Looker / Dr. Reimer & Malaki)

Eric Breker (Misc Characters / Colonel Reynolds)

Raoul Ganeev (Russian Guard / Lt. Colonel Sergei Evanov)

Tom McBeath (Misc Characters / Harry Maybourne)

Peter LaCroix (Misc Characters / Ashrak & Kendrick)

Kevin McNulty (Agent Fuller & Others / Dr. Warner)

Colin Cunningham (Misc Characters / Major Paul Davis)

Glynis Davies (Misc Characters / Ambassador Noor)

Dmitry Chepovetsky (Misc Characters / Russian Soldier)

David Lewis (Misc Characters / Cameron Balinsky)

Robert Lewis (Misc Characters / Dr. Peter Tanner)

Jay Acovone (Duffy Haskell & Det. Curtis / Major Charles Kawalsky)

Brent Stait (Timothy Mayhew / Major Louis Ferretti)

Colin Lawrence (Officer / Major Lawrence & Major Waren)

Willie Garson (Henry Weems & Quinton 'Roach' Freely / Martin Lloyd)

Robert Wisden (Robert Patrick Modell / Lt. Colonel Bert Samuels)

Matthew Walker (Arlinsky & Dr. Ronald Surnow / Merlin

Don S. Davis (Captain William Scully / Major General George Hammond)

Colleen Winton (Misc Characters / Misc Characters)

George Touliatos (Dr. Katz & Larry Winters / Pyrus & Shamda)

Tom Butler (CIA Agent Ambrose Chapel & Benjamin Drake / Major General Trofsky)

Gerard Plunkett (Dr. Calderon / Nem & High Councilor Tupl)

Jay Brazeau (Dr. Daly & Prof. Varnes / Harlan)

Jerry Wasserman (Dr. John Grago & Dr. Plith / Whitlow & Chief Of Staff)

Fulvio Cecere (Priest & Aide / Colonel Davidson)

Stuart O'Connell (Cop / Tommy Levinson)

Suleka Mathew (Agent Caleca & Lisa Dole / Kali)

Ian Robison (Detective Smith & Ranger / Frank Mitchell)

Michael Rogers (Lt. Griffin & Crewman / Misc Characters)

Roger Haskett (Deputy Dennis Tyson & Coroner / Dr. Thompson)

David Palffy (Dark Man / Anubis)

Kimberly Unger (Joan Gauthier & Karen Koretz / Nurse)

Bob Dawson (Phil Rich & Iskendarian / Bynarr)

David Hurtubise (The Pathologist & Barrington / Dr. Kleinhouse & Tomis)

Andrew Airlie (Attorney & Rob / Dr. Carmichael & Kalan)

Mar Andersons (Jack Hammond & Halverson / Bob)

Igor Morozov (Pudovkin / Russian Soldier)

Kurt Max Runte (Misc Characters / Col. Kirkland & Major Boyd)

Sean Campbell (Cop & Soldier / Solek & Sergeant)

Amanda Tapping (Carina Sayles / Major Samantha Carter)

Teryl Rothery (Michelle Charters / Dr. Janet Fraiser)