Kanjite Knight, the opening of Shin Mazinger is actually by a band called "ULTIMATE LAZY", which is basically everyone from JAM Project plus several other legendary vocalists... because it was the only way to make the group more Hot-Blooded and awesome.
On his own, Hironobu Kageyama tends to create EXTREMELY badass theme music for any anime he's involved with, part of the reason he's the current leader of JAM Project Heats, the second opening from Shin Getter Robo - The World's Final Day is quite possibly one of the ones that puts him at number one in many fans' hearts.
Yoshiki Fukuyama is also the singing voice of one Nekki Basara; that's right, that means that this guy is also the front man for a band known as Fire Bomber.
Masami Okui can hold her own among the rest of the boys: there's a reason why Revolutionary Girl Utena's "Rinbu - Revolution" is a staple at most anime song concerts. She's also the producer of the annual Animelo Summer Live concerts (the biggest anime theme song concert in Japan), which are basically an excuse to get as many of the songs on this page as possible together in one concert, short of having the universe collapsing into a singularity of awesome.
Masaaki Endoh has done a cover of both God Knows and Sora-iro Days. We all know that although they were originally sung by women, they are still awesome and hotblooded, especially to those who have seen its usage in its originalanime. Let's just hope neither of them covers happily ever after... It'll be too awesome.
To wit: Hironobu Kageyama singing "Cha-La" from Dragon Ball Z, Yoshiki Fukuyama singing (and playing guitar!) "Planet Dance" from Macross7, Hiroshi Kitadano singing "We Are" from One Piece and Masaaki Endoh singing "Yuusha-oh Tanjyo" from GaoGaiGar. That sound is your cerebral cortex melting.
"Ima Ga Sono Toki Da", the first theme to Getter Robo Armageddon by the damn-near legendary Ichiro Mizuki (co-founder of JAM Project). It has an old-school "Imperial Japanese Army March" that makes it one of the few songs that you can perform While dressed like M. Bison.
The first of those openings, "Vanguard", was used as an insert song for Koutei's Great Daiyusha Superior Crossride Final Turn against Ren in Season 2. The moment was made so balls-out awesome that even fans who utterly despise Season 2 consider that one scene awesome incarnate.
Hironobu Kageyama, Masaaki Endoh, and Hiroshi Kitadani get together as "The Manga Trio" and perform Don't Say Lazy, the K-On! ending.
Clearly, the only reason their version of the Puella Magi Madoka Magica opening theme, Connect, is in acoustic guitar is because rendering the song in their usual Hot-Blooded rock would have caused the Universe to spontaneously implode. Still balls-to-the-wall awesome.