Note: To help refresh your memory, wiki links are provided for characters when available.
LOST - "LA X"
David H. Lawrence guest starred as 'Paul,' the cab driver. You had to be quick to catch this one, but he was the driver of the cab the 'alternate timeline Kate' hijacked and 'alternate timeline Claire' was already riding in. Heroes fans will recognize him as 'Eric Doyle,' the puppeteer.
Human Target - "Sanctuary"
Sam Huntington guest starred as 'John Gray,' the guy who was hiding out at the monastery. You may recognize him as 'Jimmy Olsen' from Superman Returns.
Criminal Minds - "Parasite"
Valerie Cruz guest starred as 'Brooke Sanchez,' the woman that was scammed and impregnated by the con man under his identity of "Hunter." You might recognize her as 'Isabel' from True Blood or 'Sylvia Prado' from Dexter or even 'Lt. Connie Murphy' from The Dresden Files. She also briefly guest starred as 'Selena Ramirez' on Dollhouse.
The Vampire Diaries - "Children Of The Damned"