Withnail & I (Two failed English actors go on holiday "by mistake" to the countryside. Almost worth the price of admission just for some of the lines their dealer comes out with.)
Carlito's Way (This movie nearly made me cry. It's like Scarface, except less over the top, with a much more sympathetic protagonist and, well, just plain better.)
It's A Wonderful Life (A man on the verge of killing himself is given the chance to see what life would be like in his hometown had he never been born. A perennial favourite.)
Platoon (SEE THIS NOW. THIS IS NOT A POINT TO BE NEGOTIATED.)
Kundun (A too often overlooked Scorsese film about the Dalai Lama prior to his exile. Arguably a bit hagiographic, but amazing nonetheless.)
Bright Young Things (An adaptation of Evelyn Waugh's Vile Bodies and Stephen Fry's directorial debut. That alone should be enough to make you run out and see it as quickly as possible.)
Good Bye, Lenin! (A German film about the final days of East Germany. A woman dedicated to the socialist cause falls into a coma, but soon recovers. However, the doctor informs her son not to surprise or shock her in any way because it could be fatal. The fact that the Berlin Wall has just fallen presents something of a problem, and the son endeavours to create a miniature pretend East Germany in his mother's apartment.)
And that's just a few. There are many, many more great films out there just waiting for you to see them, so, you know, get out there.