I'm a bit old skool:
Andy Lau Tak-Wah (because he makes about six films a year and so keeps me in good drama/thrillers/actioners),
Aaron Kwok Fu-Sing (because he doesn't make many movies any more, but when he does they're awesome - Cold War 1 and 2, Port of Call, the three Detective movies, Peace Breaker [a remake of the Korean film A Hard Day] etc.),
Donnie Yen Chi-Tan (because he's just all-around awesome, and his movies have great rewatchability!),
Sammi Cheng Sau-Man (great comic timing but also has the ability to smack you with mood whiplash),
and now I've got a way to watch HK dramas:
Kenneth Ma Gwok-Ming (just finished 2 TVB dramas and he happened to be in both. Awesome),
Matt Yeung (can't wait for more from him).