repeat offenders

Here is a list of people I've seen in both X-Files and Stargate, in less-than-exact order.

Seasons 1-7

Kevin McNulty
Tom Butler
Blu Mankuma
Glynis Davies
Don S. Davis
Marshall Bell
Jason Schombing
Jay Brazeau
Robin Mossley
Peter LaCroix
Tom MacBeath
Mitch Pileggi
William B. Davis
George Touliatos
Tony Todd
Steven Williams
Paul McGillion
Teryl Rothery
Megan Leitch
Colin Cunningham
Bill Dow
Steve Bacic
Alex Diakun
Willie Garson
Thomas Kopache
Nancy Sorel
Jewel Staite
Gillian Barber
Kenneth Welsh
Robert Wisden
Amanda Tapping
Sebastian Spence
Marie Stillin
Chris Owens
Hiro Kanagawa
Michael Puttonen
Jay Acovone
Barry Levy
Gerard Plunkett
Peter Williams
Peter Kelamis
Brent Stait
Peter Stebbings
Ellie Harvie
Brian Markinson
Brad Lowe (? can't read own writing)
David Lewis
Roger R. Cross
Hrothgar Matthews
Tobin Bell
Tony Amendola

Also John Deihl from the original Stargate movie. I couldn't decide if he counted or not.

I remember Robert Patrick, Adam Baldwin, and Matthew Glave from seasons 8-9.

These are just the people I recognized.