If one defunct band...

Hexen, I love the direction that band was going. There are a lot of other good options but a lot of bands were also going downhill when they split up. Ozzy featuring randy rhoads would be another good choice.

Non metal umm Michael Jackson or Queen?
 
Metal: Botch, but really most reunion albums suck and most of the bands I wanted to release reunion albums did. And they sucked. So maybe no one actually.

Non-metal: Jeff Buckley or Jimi Hendrix because they both had so much more to give creatively that we never saw and it's a fucking shame.
 
I was gonna say that the crossover/thrash lineup of English Dogs should reunite and do another album, and then I discovered that they did last year, haha! Now to find out if I should be more careful of what I wish for.
 
Zyklon
[ame]http://youtube.com/watch?v=9ojfUcR6znc[/ame]

Despised Icon
[ame]http://youtube.com/watch?v=mUaAjEB3acg[/ame]

The Calling
[ame]http://youtube.com/watch?v=pnUEiEW8lmc[/ame]