Great film, yes -- WarGames. He's only in it for about 5 minutes and I wouldn't really count this as an 'under the radar' film, but most people forget/don't know he's in it. And if you've never seen it, it really is an excellent film.

Slow Horses by Mick Herron. I watched the series and now I've started the book series. Very British and very sarcastic, so it's been really good so far.