Well my picks, as a fan of European-style melodic Metal:
Lead Vocals -
Russell Allen (Symphony X). This guy is THE man, hands down. From power metal vocals, to (still harmonic) growls, to musical-style singing with a soul touch in his voice; this guy delivers everything any band could ever need. Whatever you want - you bet this guy can do it. And he just blows everything away live too, and just in the studio where you can do a lot of tweaking and what not. This man is as good, if not better, in the live situation and delivers everytime. Bow down to the master

(On a side not, a close second would also have been Freddy Mercury for me; one of the most charismatic front men of all time, plus a very good singer. And another option the prototype Power Metal singer - Mr Ronnie James Dio.)
Guitar 1 -
Michael Romeo (Symphony X). Again, have to pick an Symphony X guy, but this dude is too amazing to be left out. With a smile on his face, this guy makes every supposed guitar hero feel ashamed of himself and wanting to go back to his room for another couple of years, just to practice. Well maybe with the exception of John Petrucci

But again, what makes Romeo win is that he can play both interesting rhythm parts, and killer speed solos, and always work FOR the song, and not only for his guitar playing, something that I feel happens all too often with Prog Rock/Metal guitar players (and Mr Petrucci is no exception there). So my vote goes to him.
Guitar #2:
Victor Smolski (Rage). Probably the best all-around guitar player I know. Has a tremendous sound, plus can play really groovy rhythm parts as well as killer solos, and also always plays very song-serving. While Michael Romeo may be a bit better in the pure technical department, Smolski definitely outdoes pretty much everyone on the "feeling" side of things, especially for a metal guitarist. I guess he could be the metal equivalent of Slash
Bass: Hm there are a couple of guys who are really good bass players, however few true standouts... Which of course has also to do with the fact that the bass just isn't such a prima facie high profile part of a band (although a tremendously important one). Currently, I would pick
Lauri Porra from Stratovarius. Young guy, insane on the Bass. Other picks would be Joey DeMaio (Manowar), simply for his extravagant persona and unique basses and playing style, or probably Felipe Andreoli (Angra). Also, I feel that John Deacon (Queen) deserves a mention here; even if the Queen songs weren't that technically challenging for the bass player most of the time, he came up with some great bass lines nonetheless.
Drums: Hm I kind of like
Mike Terrana (currently Masterplan), as a pure power metal drummer. On an overall scale, I also could live with Aquiles Priester (Angra), since he has a good groove, or Ian Paice from Deep Purple, if we delve into history a bit.
But well, there are many constellations of "dream bands", I guess I more or less made a dream-"metal"-band... if I were to vote strictly for (Hard) Rock musicians, it would look a bit differently.