There are certain films that fall into this category for me and they are an odd bunch:
The Poseiden Adventure (original)
The Great Escape
Where Eagles Dare
The Jokers - a pretty obscure 1967 Michael Winner film (I know!)
Pirates of the Caribbean (1 & 4)
Sherlock Holmes Game of Shadows
Tron Legacy
X Men: First Class
Master and Commander
Live and Let Die
I, Robot
Downfall
Rocky II
The Bourne Identity and Supremacy
When I really like a film I enjoy it more the 2nd, 3rd and 4th time around. The law of diminishing returns tends to kick in after that point.
Edit: Forgot
Snatch
Lock Stock and Two Smoking Barrels
2nd Edit: Completely forgot the ones I've watched the most
Alien, Aliens, Predator, Predator 2 - and to my eternal shame, Aliens vs Predator.