Amanda Tapping - Sanctuary (ended with 4th season)
Rainbow Sun Francks - The Listener (joined in second season)
Robert Carlyle - Once Upon a Time
Jewel Staite - The L.A. Complex
Michael Shanks - Saving Hope
Additionally, some of our Stargate guest stars have also made it to regular starring roles. I can't list them all, but a few that jump out at me at the moment are: Ben Bass in Rookie Blue, Erica Durance in Saving Hope (producer and star), Lou Diamond Phillips in Longmire, and Tony Amendola in Once Upon a Time (recurring).
Let me know if I missed anyone!