Marvel Comics:
* The Big Three: Spider-Man, Captain America, Iron Man
* Avengers: Thor, Hulk, Black Widow, Hawkeye, Scarlet Witch, Vision, War Machine, Black Panther, Captain Marvel, Ant-Man, Wasp, Doctor Strange, Ms. Marvel, Wolverine
* X-Men: Cyclops, Wolverine, Storm, Jean Grey, Professor X, Beast, Nightcrawler, Gambit, Rogue, Iceman
* Other Heroes: Daredevil, Punisher, Ghost Rider, Silver Surfer, Fantastic Four (Mr. Fantastic, Invisible Woman, Human Torch, Thing), Deadpool, She-Hulk, Moon Knight, Shang-Chi, Blade, Doctor Doom (anti-hero)
DC Comics:
* Justice League: Superman, Batman, Wonder Woman, Aquaman, Flash, Green Lantern, Cyborg, Martian Manhunter, Shazam
* Other Heroes: Green Arrow, Black Canary, Hawkman, Hawkgirl, Booster Gold, Blue Beetle, Plastic Man, Firestorm, Atom, Teen Titans (Robin, Starfire, Beast Boy, Raven, Cyborg, Kid Flash)
* The Watchmen: Dr. Manhattan, Nite Owl, Silk Spectre, Rorschach, Ozymandias
* Other Notable Characters: John Constantine, Swamp Thing, Zatanna, Catwoman, Harley Quinn (anti-hero)
Other Publishers:
* Image Comics: Spawn, The Walking Dead (Rick Grimes, Daryl Dixon), Invincible, Saga (Alana, Marko)
* Dark Horse Comics: Hellboy, The Umbrella Academy (Spaceboy, Vanya Hargreeves), Sin City (Marv)
* Valiant Comics: Bloodshot, X-O Manowar, Shadowman, Faith
This is just a small sample of the many, many comic book heroes out there. Feel free to ask for more specific categories, or for names of heroes from a particular era or publisher!