I guess it is a toss up between Senna, Moon, and Good Night, and Good Luck for me.
Terminator 2 - I watch this at least once a year, and I just think it's a perfect early 90s action movie. And it has Arnie!
Letter Never Sent - Gorgeously shot movie about geologists searching for diamonds in Siberia. It's kind of like The Revenant, sorta, but filmed over fifty years ago.
Kung Fu Hustle - I love Stephen Chow movies, and I think this is probably his best. I also think God of Cookery and Shaolin Soccer are fantastic. It's a shame his more recent offerings haven't been quite as good. That Hong Kong slapstick just gets me.
Kind Hearts and Coronets - because you get to see Alec Guinness play eight different people. Speaking of Alec Guinness, The Bridge on the River Kwai.
Anyway that's all I can think of right now.
Edit: I just finished watching Gangs of Wasseypur, which is easily the longest movie I've ever watched - nearly five and a half hours long (and I thought Gone With the Wind was a drag). It's an Indian gangster movie set over three generations, so there's a lot going on. Plenty of murder and double-crossing and vengeance, but it's Bollywood too so there's some music thrown in. I wouldn't say it's a favourite, but it's worth checking out (it's split into two parts, thank Christ; Indian cinemas apparently wouldn't run the full movie, for obvious reasons.)