An interesting thing to try to do is to split up the PCs. No, not physically, but in terms of what they want to achieve, or even what side they are on.

Normally, the players in a game work together. When they encounter a villain, don't have the villain offer them something that they all might conceivably want in exchange for not opposing him. Offer something that one of the players' characters will find irresistible.

Divide and conquer. Sow discord amongst the PCs and watch them bicker about whether they should accept the villain's offer or stick together and defeat his evil plans. The good thing is this barely takes any effort for most groups of players.

Transcript

Combat Cyborg: Here are their hitty stick things.
General Grievous: Ah, a fine vintage. Tones of cobalt, silvery, but with a cadmium finish. Shame about the second one.
Anakin: The first was definitely mine.
General Grievous: And a droidling too. A messiah's work is never done.
Obi-Wan: What do you mean?
General Grievous: Although they are unworthy organ-buckets, I shall grant them a great boon.
Obi-Wan: I'm afraid to ask.
General Grievous: Do you know what it takes to create a perfect being?
R2-D2: You're looking at one, baby.
General Grievous: Only in your reflection.
General Grievous: Change places!
General Grievous: Bring forth the cyber-emulsion arc-saw!
R2-D2: If you're planning to give me one of those, I for one would like to bow to my new cybernetic master.