It's a mystery worthy of the world's Greatest Detective — why on Earth does Batman bother wearing a cowl? It's not like he tries that hard to keep his identity secret — there are literally dozens and dozens of people, good, evil, dumb, and random, who know Wayne is traipsing about in a bat costume. Here's a just a small, small assortment,
The Bat-Family: Back when Bruce Wayne became Batman, only one person knew the hero's true identity — his faithful butler Alfred. When Bruce decided to adopt the newly orphaned Dick Grayson and train him as his sidekick, Robin also discovered the secret. But slowly, the Bat-family grew, encompassing three other Robins, including Jason Todd, Tim Drake and Bruce's own son Damian; three Batgirls, including Barbara Gordon, Cassandra Cain and Stephanie Brown; Azrael, who served as Batman for awhile. WayneTech's R&D head Lucius Fox knows, obviously, and although Commissioner Gordon has never outright admitted it, he almost certainly has to know who he's been dealing with all these years or he's be the worst detective ever.
Other Heroes: It would make sense that Batman would revealed his identity to a few of his closest superhero friends, such as Superman and Wonder Woman. Maybe the entire Justice League thought it would be best to all come clean and reveal their identities, which is why The Flash, Green Lantern, Green Arrow, Martian Manhutner, Hawkman and Hawkgirl, Aquaman, and more. And then maybe everyone who joined the Justice League got some kind of contact info sheet for all the other JL members, which is how lesser heroes like The Atom, Black Canary, Black Lightning, Blue Beetle, Booster Gold, Cyborg, Deadman, Plastic Man, Red Tonnado, Supergirl, Zatanna, and more. Also, The Phantom Stranger and The Spectre both know Bruce's secret, but they're basically omniscient so there's not much to be done about that.
The Teen Titans: Hilariously, upon entering the Teen Titans, Dick Grayson apparently went out of his way to tell ALL of his new teammates about Batman's true identity. Starfare, Raven, Beat Boy, Donna Troy, and Terra. Seeing as Terra was actually Deathstroke the Terminator's evil sidekick in disguise, this was a bad idea. Loose lips sink Bat-ships, Robin.
Lovers: You know, for a solitary loner focused wholly on his quest for vengeance, Batman seems to have a lot of time for fucking. He's had a long-time on-again, off-again relationship with on-again, off-again villainess Catwoman, who very much knew who her lover was behind the cowl prior to the New 52 reboot. And Talia Al'Ghul, daughter of villain Ra's Al Ghul and mother to Bruce's child Damian, also obviously knew her baby-daddy's identity. One of Bruce's first gal-pals in the comics, a socialite named Silver St. Cloud, spent so much time up-close-and-personal with Bruce's faces she eventually recognized the true owner of Batman's jaw, In the movies, every single love interest gets to know Bruce's night-jon, no matter how useless they are — it's not so bad when reporter Vicki Vale figures it out, or Catwoman, but by the time Nichole Kidman and swimsuit model Elle MacPherson are let into the Batcave, you have to wonder why Batman bothers keeping his secret from anybody. This even extended to the animated Batman movie, as Bruce's first love Andrea Beaumont, after she saw Batman at the Wayne family grave (still the only Batman romance that ever needed to be film, by the way).
Villains: But so far, all the people who know Batman's secret like Batman (well, mostly; Talia Al Ghull is not always a fan). Alas, countless of Batman's foes know Bruce Wayne is their real archenemy. This includes Bane, who recognized the truth by realizing Batman's body language was the same as Wayne's; Deathstroke, a happy by-product of his figuring out who Robin/Nightwing was; the telepathic Despero; the Riddler, who also told Hush; Man-Bat's alter-ego Dr. Kirk Langstrom; Max Lord, thanks to his super BrotherEye spyware; Ra's Al Ghul and his other daughter Nissa, in addition to Talia, of course; and a whole ton of villains that Zatanna ended up mind-wiping in the retcon of the Identity Crisis debacle. Additionally, Dr. Hugo Strange always acts like knows Bruce Wayne is Batman, but he's never actually said it out loud or been in the same room when Batman has taken off his cowl, Batman's evil Earth-3 doppelganger Owlman knows, because Owlman was Bruce's brother in his reality, and thus it was pretty easy to put 2 and 2 together. Also, it seems very, very likely that the Joker knows, but just doesn't particularly give a shit. Batman is his focus; Bruce Wayne just bores him.
Others: Why stop there? Why not let more people in on Batman's true identity? Here's just a few:
• Sherlock Holmes figured it out before he ever met Batman (which has happened on occasion, of course). He's Sherlock Holmes; of course he figured it out
• Lois Lane knew back in the continuity where she was married to Superman, because that's how Superman rolls.
• That weird Mr. Reese accountant guy from Nolan's Batman movies seems to know, although this doesn't really amount to anything.
• The current Huntress in the New 52-inverse is actually Helena Wayne, the daughter of Bruce Wayne and Catwoman. Since she's running around as a superhero, she probably knows her dad's secret. Else it's one hell of a coincidence.
• Bruce Wayne revealed his identity to Joe Chill, the random hood who killed his parents, before he enacted his final revenge. But a terrified Chill got away and asked some fellow criminals to protect him. Upon learning why Batman had a mad-on for him, these criminals were so pissed at Chill for creating Batman and making their lives hell they actually beat him to death before anyone even thought to ask him what Batman's identity was.
• Aunt Harriet, best known from the '60 TV series, actually appeared in the Batman comics for a bit. At one point she stumbled upon the elevator to the Batcave and realized her nephew Bruce and his ward Dick must be Batman and Robin! Then Bruce and Dick got home and managed to convince her that in fact they were just good friends with the Dynamic duo, because Aunt Harriet is an imbecile.
• The evil Killer Moth once got plastic surgery to impersonate Bruce Wayne, and, whilst in Wayne Manor, also happened to wander down to the Batcave. Before he can do anything with the information, he's shot in the head, and a doctor has to remove part of his brain — the portion that just so happens to include information regarding superheroes received in the last 24 or so hours.
• Leslie Thompkins was a friend of the Wayne family who dedicated her life to helping the poor of Gotham City. She has treated Batman medically on many an occasion and knows Bruce's secret, although she's not a fan of his vigilantism. There was a also a super-weird thing where she pretended to let Stephanie Brown die to "teach Batman a lesson" but the less about that the better.
• Bruce Wayne straight up tells Superman's pal Jimmy Olson his identity. Why? Because Jimmy asked.
• The animated hero Static Shock figured it out when he realized Bruce Wayne was visiting his friend Allie, whom Batman had just saved, in the hospital. This makes Static Shock the smartest person in the entire DCAU.
• The Shadow knows. Duh.