I find it hard to give a definitive top-ten as my favourite film at a given time can largely depend on my mood. Films that I tend to have jostling about as part of a top-ten would be (in no particular order):
Empire Strikes Back
An American Werewolf in London
Rear Window
The Exorcist
The Outlaw Josey Wales
Jaws
The King of Comedy
Raiders of the Lost Ark
One Flew Over the Cuckoo's Nest
The Thing
I could probably give about 2-300 films that I really love, but they're the ones that I could watch then rewind (as it were back in the day of VHS) to watch again.