Where does Clark watch for travel deals?

Clark always talks about traveling to where he finds the deals. Where is he monitoring to catch these deals? I would specifically like to watch for travel from US to Europe. I considered trying Going (Scott’s Cheap Flights), but in order to get international deals you have to sign up for the premium service at $40/year. Thought I’d see if anyone had free recommendations before committing to the $40. Thanks!

GOING.COM is what Clark uses, and Google Flights I think