Dying isn't fatal, when death does occur

[DrSavant]

If you ever have had some villian in your
game die and want to bring them back
(short of "'he wasn't really dead" )
here are some ideas;

1) Person is Reincarnated [Thunderbolts]

2) Person is replaced by someone else
using same costume and name.
[ SpyMaster,The Phantom]

3) Person's spirit lives on after them
[ DP 7 's The Watcher]

4) Person enters alternate reality
[ Mutant X ]

5) Person's focus is given to another
[ Green Lantern]

6) Person is brought back to life
[too many to name]

[Hermit]

While perhaps just variations on what you've already covered, don't forget:
Cloning, it's not just for sheep any more.
Down loading your brain into a computer/robot
Someone goes back in time and 'saves' the villain (Or, even more ironic, the super heroes go back, and one side effect is the fiend lived)

[Evil Steve]

Don't forget the ever popular vast cybernetic reconstruction. That one got me out of a corner.

[Patriot]

Re-animation by a not so good group(say Duchess)

Many great story arcs can come out of this one.