Tricky one this. I'm not necessarily talking about quality of movie, although they are all superbly made in my opinion, but movies that I can watch over and over again and not get tired of, cringed-out by or downright annoyed by about a particular decision or other. I can enjoy them as much as I did the first time I saw them. Sort of desert island movies - these are the only movies you can watch so you'd better choose well.
Here goes, and in no particular order...
Chariots of Fire
Platoon
Trainspotting
Four Weddings & a Funeral
Life of Brian
Gladiator
Lawrence of Arabia
Henry V (1989)
Forrest Gump
Saving Private Ryan