Shawshank Redemption
Lawrence of Arabia
LA Confidential
Alien
Some like it Hot
The top two are true stories which somehow seems more significant. Sadly most of those are American. Spielberg's best stuff is brilliant but a bit cheesy at times so don't make my favourite 5.
There are loads of British films I love especially the old black and white Ealing comedies but these seem a bit twee these days and the more recent stuff is well acted or made technically but a bit too luvee to be in my top 5.