I'm going to see Queen + Adam Lambert this summer, really looking forward to it! I love Adam, but of course I would have loved the opportunity to see Freddie.
AC/DC is coming back, so you may still get the chance to see them. I got to see them a few times on their Black Ice tour. I had 3rd row in Nashville, it was awesome!
I wish I had been able to see Elvis and Michael Jackson. My top bucket list band that is still active is Tyketto.