Giving something a 10 to any film is very difficult indeed, as it would be saying that I find said film flawless. I think the only film I have ever felt this way about is the Shawshank Redemption. There is simply nothing I would change in that film. Others that I would consider 9.5s include...
Back to the Future 1 & 2 (Twoof my favourite films. Almost perfect, let down only by the dated-ness of seeing them now, as I only saw them for the first time a few years ago. I think if I'd seen them back in the 80s or early 90s they would have been a 10 then. So that's really my fault rather than the films').
The first two of the LOTR trilogy (I don't really like the third one, even though it is often regarded as the best of the three. I felt there was something missing in the third one, it had just lost the spark of the first two. It just seemed... odd. But the first two, particularly the Two Towers, are wonderful, marked down only by brief moments of sluggishness).
This is Spinal Tap (I was not expecting to particularly enjoy this film when my boyfriend watched it, but I was completely proved wrong. I absolutely loved it, yet whilst I cannot say exactly what flaws it has, I do not consider it to be quite perfect).
Forrest Gump (for all its ridiculous schmaltzy-ness, I love this film. I grew up loving it, so perhaps that is partly why I rate it so highly, but I think it is near perfect.)
Toy Story 1 & 2 (I feel the first spenRAB slightly too much time in Sid's house and is slightly more stagnant than the second, although I feel that the second doesn't have quite the same spark that the first has, probably just becaue it's the first. Otherwise they would both be 10s. Almost all Pixars actually would be high 9s, especially Wall.e, Monsters Inc and Up, although they do have their flaws).
And possibly some others. I will have to go away and think about it.