If you are going to use the last design (which I don't recommend, the Vader one was very good) at least make the lines less defined, give it a blur, a fading transition from the solid black on the front to the crimson red on the back - sharp-cut lines are not attractive, nor are they very professional - that's liek the difference between MS Paint and Photoshop! :p
I'm not saying I can do any better, but I can say what I find to be visually and aesthetically (sp?) pleasing. Although Vader is oyur best bet atm, If you really want to go all out for this project and get oodles of E.C., go for a collage. For example, look at the Ep 1 and II DVD art:
Notice how the how cover is eye-catching, rish with detail. Although there is a focus (Anakin), attention to detail is also shared among the other characters and scenery - there is no "absolute" center of focus, there is a good distribution of variety and action all over.
Now I'm not suggesting you should make a "clone" (no pun intended) of the other two boxes, but at the same time, look at them for ideas. Most "epic" moveis with a large ensemble cast use this method of art, and I've always foudn it highly effective. Just look at Indiana Jones!
However, if you want to be different, you could make a less flashy but more dark and foreboding cover, for example, look at the Godfather:
Notice the symbolism, the timeless yet simple figure that says so much without the need for explosions and dramatic portraits - show most people over the age of 50 this cover, and they'll instantly associate it with a classic movie. Sometimes less is more. If you're wondering what symbol you could use, it could be a variation on Vader's helmet, his cape, or it could even be the Imperial Symbol. All sorts of things you could do.
I could think of more ideas, but here are few things you might like to consider. I'm no expert, but this is just what occurred to me.