http://www.pajiba.com/trade_news/a-...bs-top-250-currently-available-on-netflix.php
Also, there's this for good films, since so far people have mostly suggested TV shows. IMDB has a great balenced list of films in the top 250, and these are probably all well worth watching.
1. Pulp Fiction
2. Forrest Gump
3. Once Upon a Time in the West
4. Life Is Beautiful
5. Memento
6. Terminator 2: Judgment Day
7. Apocalypse Now
8. The Pianist
9. Cinema Paradiso
10. Amelie
11. Double Indemnity
12. Reservoir Dogs
13. Oldboy
14. Witness for the Prosecution
15. All About Eve
16. The Apartment
17. Some Like It Hot
18. Raging Bull
19. Downfall (Amazing foreign film, but is some heavy stuff)
20. The General
21. Lock, Stock and Two Smoking Barrels
22. Fargo
23. Rang De Basanti
24. Warrior
25. Trainspotting
26. Hotel Rwanda
27. Butch Cassidy and the Sundance Kid
28. Into the Wild
29. The Grapes of Wrath
30. Mary and Max
31. High Noon
32. There Will Be Blood
33. Donnie Darko
34. The King’s Speech
35. Hachi: A Dog’s Tale
36. Ip Man
37. Pirates of the Caribbean: The Curse of the Black Pearl
38. The Man Who Shot Liberty Valance
39. Elite Squad: The Enemy Within
40. The Truman Show
41. Departures
The bold ones I've seen and recommend. Some great cinema you can get covered there, and I'd encourage you to use the Top 250 as a way to find new directors and genres you like even on disk.