Many should be recognized IMO, I will quote some that strikes my mind right now:
Best lyricist in English language: Martin Walkyier (Sabbat, Skyclad, Clan Destined)
Great composers
Bruce Dickinson (solo, Iron Maiden)
Rob Halford (solo, Judas Priest)
Ronnie James Dio (solo, Black Sabbath, Rainbow)
Phil Lynnot (Thin Lizzy)
Anthony Arjen Lucassen (Vengeance, Bodine, Ayreon, Star One, Ambeon, Stream Of Passion)
Steve Harris (Iron Maiden, specially old ones)
Rick Wakeman (solo, Yes)
Derek Sherinian (solo)
Lemmy (Motorhead)
Jorn Lande (Jorn, Ark, Millenium, Masterplan)
Roger Waters (Pink Floyd)
Nibbs Carter (Saxon)
Great composing teams
Graeme English/Steve Ramsey (Satan, Pariah, Skyclad)
Iommi/Butler/Ward (Black Sabbath)
Gillan/Blackmore/Lord/Paice (Deep Purple)
Tipton/Downey/Halford (Judas Priest)
Smith/Dickinson (Iron Maiden, Bruce Dickinson)
Schaeffer/Kusch (Demons & Wizards)
Lee/Peart/Lifeson (Rush)
Kilminster/Campbell/Dee (Motorhead)
Petrucci/Portnoy (Dream Theater)
Tatler/Harris (Diamond Head)
Roeser/Pearlman/Bloom (Blue Oyster Cult)