Nobody has mentioned this yet...
It's quite brilliant. It's a 'con' film about two confidence tricksters.
It's one of the favourites, probably only behind City of God, which frankly, is amazing.
I'll second a few more which have already been listed....
Amores Perros - Good film, but loses it's way with the over-indulgence on the girl in the wheelchair and her stupid dog.
Y Tu Mama Tambien - Great road movie. JUst a nice film, with sex in it.
City of God - Amazing
City of Men - Not as good as City of God, but still very decent.
Elite Squad - Again Brazilian, about the corrupt police force. Very decent imo.
A Prophet - Quality film about an Algerian serving time in prison. Basically becomes 'the shit' when inside. Top quality film with nas on the soundtrack as well :-)
La Haine - Shot in black and white. Follows a gang of lads in a French Suburb. Great cinematography. Good film.
OldBoy - Quality film.
I'll throw a few more lesser known ones into the mix aswell.
The Man of the Year
It's not the American one with Robin Williams. It's a Brazilian one with a guy with daft hair. He ends up killing the local gangster. Rather than being punished for it he becomes the town's hero.
Drama/Mex
I'm not going to lie. I bought this film because it had Diana Garcia in it and i'm a pervert. It's a quality film though. Set in Mexico. Sex, drugs, violence. You get the picture.
Sin Nombre
Again this film has Diana Garcia in it at the start for a while. It's about a family of immigrants who are trying to illegally enter the USA. The immigrant train gets robbed and the lead character loses her family. She befriends one of the robbers. It's a quality film. One of my favourites.
Lower City
Another Brazilian film this time about 2 best mates who fall for the same hooker. Loads of sex in it. It's more or less porn. It's half decent though.
Tsotsi
South African film about a young lad who steals a car. Unfortunately for him there is a baby in the back seat. He looks after it. It's quite moving. Really good soundtrack aswell. Good film. Quite sad at the end.
Fateless
A really depressing film about the Holocaust. Probably don't watch it if you're in a good mood. It is a very good film though. Quite upsetting til Daniel Craig pops up at the end (before he was famous i think).