1. Empire Strikes Back
2. Revenge of the Sith
NOTE: Earlier I had these two in a tie... I think, however, I'd always have to give the edge to ESB, simply because of the presence of Han Solo.
3. A New Hope
4. Return of the Jedi
5. The Phantom Menace
6. Attack of the Clones
Also, I'd like to note that in my ranking of all time great films, the entire Star Wars saga ranks as #1 (I lump them together to keep it as simple as possible), followed by the Indiana Jones series, Godfather 1 & 2, Rocky (1 only), etc.