At this moment in time:

1. Notorious
2. Shadow of a Doubt
3. Rear Window
4. Rebecca
5. Psycho
6. 39 Steps
7. The Lady Vanishes
8. Frenzy
9. Strangers on a Train
10. North By Northwest

The first two stand above the rest. I could add other really interesting films e.g. Marnie, Vertigo, Bon Voyage etc.