Dooku was a must. So many posters/wallpapers prefer using Grievous and neglecting Dooku, but Dooku was more important to the plot of Anakin's downfall, and he was an actual Sith (in a movie called Revenge of the Sith). And he's Christopher Lee. Christopher Lee.
I love both trilogy finales (Return of the Jedi and Revenge of the Sith) the most of all the Star Wars films, though I love all the films pretty much equally, and depending on my mood of course. There's a sense of profound destiny, an inescapable conclusion in both the ascendancy of the Sith and the return of the Jedi that makes the end films of both trilogies so much...fun.