Updating this list:
Doctor Strange - Dr. Fate
Hulk - Swamp Thing
Namor - Aquaman
Silver Surfer - Firestorm
Valkyrie - Shining Knight (from Morrison's Seven Soldiers)
Hellcat - Crimson Fox
Hellstorm - Faust
Gargoyle - Etrigan
Beast - Tasmanian Devil
Nighthawk - Golden Eagle
Clea - Silver Sorceress
Devil Slayer - Bloodwynd
Moondragon - Maxima
Iceman - Kole
Angel - Azrael (the one from Titans)
Harbinger, Mister Miracle, Wonder Woman, Madame Xanadu and Captain Marvel/Shazam would also be semi-regulars.
Team HQ - Fate's Tower