I definitely would include Avantasia and Fates Warning, but I'm (barring catastrophe) finally going to see both this year, so I guess I'll remove them and do 5 others.
Savatage (not going to happen, but what the hell)
Bruce Dickinson (also not going to happen, because I doubt he'll ever play another solo show)
Honestly, that's a weird list but that's about it. I've been very fortunate with a lot of the shows I've seen, so with Avantasia and Fates Warning joining the list, I really have seen all of my absolute favorite bands live except for Savatage. There's also a good number of bands I've only seen once or twice that I would really love to see again (Blind Guardian, Evergrey, Riot, Pagan's Mind, UFO, etc.)
Also, sadly I never got to see Dio as a solo artist. HUGE regret/unfortunate reality.