So I tried to compile a list of all the shinobi that are or believed to be kage-level or beyond, excluding those from ancient history:
Konoha
First Hokage (Senju Hashirama)
Second Hokage (Senju Tobirama)
Third Hokage (Sarutobi Hiruzen)
Fourth Hokage (Namikaze Minato)
Fifth Hokage (Tsunade)
Uchiha Madara
Shimura Danzo
Jiraiya
Orochimaru
Hatake Sakumo
Hatake Kakashi - Possibly downgraded upon losing his Sharingan.
Maito Gai - Possibly downgraded as a cripple.
Uchiha Obito
Uchiha Shisui
Yakushi Kabuto - Post-Orochimaru.
Uchiha Itachi
Haruno Sakura - Once her Strength of a Hundred Seal was filled.
Uchiha Sasuke
Uzumaki Naruto
Suna
First Kazekage
Second Kazekage
Third Kazekage
Fourth Kazekage
Fifth Kazekage (Gaara)
Chiyo
Sasori
Kumo
First Raikage
Second Raikage
Third Raikage
Fourth Raikage (A)
Ginkaku and Kinkaku
Killer B
Kiri
First Mizukage
Second Mizukage
Third Mizukage
Fourth Mizukage (Yagura)
Fifth Mizukage (Terumii Mei)
Hoshigaki Kisame
Iwa
First Tsuchikage
Second Tsuchikage (Mu)
Third Tsuchikage (Onoki)
Deidara
Other Villages
Nagato
Konan
Hanzo
Hidan
Kakuzu
Potential Candidates
Uzumaki Kushina - Jinchuuriki, chakra chains, fuuinjutsu master, famous and implied to have fought as Minato's partner.
Maito Dai - A loser genin but able to open all Eight Gates
Rock Lee - Six Gates
Hoozuki Mangetsu - Mastered all seven swords.
Kato Dan - Aspired to be Hokage and has one hell of a killer jutsu.
Darui - Raikage's right-hand man and learned Black Lightning from his predecessor.
Dodai - Experienced, a major help against the Third Raikage and damn handy with Lava Release.
Nii Yugito - Could transform into the Two Tails and wreck shit.
Ebizou - One of the Honored Siblings.
Kankuro - Best puppetmaster in Suna (now) and overcame Sasori, but nowhere near at his best.
Temari - Best wind user in the Shinobi Alliance apparently.
Pakura/Gari - Killed some bitches.
Kitsuchi - Makes a big ass mountain and is Second Division Commander of the Shinobi Alliance. Probably Onoki's son.
Mifune - Not a ninja but he fought Hanzo.
Zetsu - what is this guy i don't even
Konoha
First Hokage (Senju Hashirama)
Second Hokage (Senju Tobirama)
Third Hokage (Sarutobi Hiruzen)
Fourth Hokage (Namikaze Minato)
Fifth Hokage (Tsunade)
Uchiha Madara
Shimura Danzo
Jiraiya
Orochimaru
Hatake Sakumo
Hatake Kakashi - Possibly downgraded upon losing his Sharingan.
Maito Gai - Possibly downgraded as a cripple.
Uchiha Obito
Uchiha Shisui
Yakushi Kabuto - Post-Orochimaru.
Uchiha Itachi
Haruno Sakura - Once her Strength of a Hundred Seal was filled.
Uchiha Sasuke
Uzumaki Naruto
Suna
First Kazekage
Second Kazekage
Third Kazekage
Fourth Kazekage
Fifth Kazekage (Gaara)
Chiyo
Sasori
Kumo
First Raikage
Second Raikage
Third Raikage
Fourth Raikage (A)
Ginkaku and Kinkaku
Killer B
Kiri
First Mizukage
Second Mizukage
Third Mizukage
Fourth Mizukage (Yagura)
Fifth Mizukage (Terumii Mei)
Hoshigaki Kisame
Iwa
First Tsuchikage
Second Tsuchikage (Mu)
Third Tsuchikage (Onoki)
Deidara
Other Villages
Nagato
Konan
Hanzo
Hidan
Kakuzu
Potential Candidates
Uzumaki Kushina - Jinchuuriki, chakra chains, fuuinjutsu master, famous and implied to have fought as Minato's partner.
Maito Dai - A loser genin but able to open all Eight Gates
Rock Lee - Six Gates
Hoozuki Mangetsu - Mastered all seven swords.
Kato Dan - Aspired to be Hokage and has one hell of a killer jutsu.
Darui - Raikage's right-hand man and learned Black Lightning from his predecessor.
Dodai - Experienced, a major help against the Third Raikage and damn handy with Lava Release.
Nii Yugito - Could transform into the Two Tails and wreck shit.
Ebizou - One of the Honored Siblings.
Kankuro - Best puppetmaster in Suna (now) and overcame Sasori, but nowhere near at his best.
Temari - Best wind user in the Shinobi Alliance apparently.
Pakura/Gari - Killed some bitches.
Kitsuchi - Makes a big ass mountain and is Second Division Commander of the Shinobi Alliance. Probably Onoki's son.
Mifune - Not a ninja but he fought Hanzo.
Zetsu - what is this guy i don't even