(at around 46 mins) The date on the invitation to the Black & White Ball Karen Page gives Matt Murdock is July 24th however the date on the invitation he finds on the pillow is August 13th.
(at around 1h 11 mins) When Elektra is practicing with her knives against the sandbags, she has a braid in her hair. When she slashes the last one and the scene is about to end, her braid is gone.
(at around 1h 35 mins) The font used in Ben Urich's "Daredevil Revealed" article changes when the deleting begins.
(at around 1h 9 mins) When Kingpin is talking with Bullseye, he has a cane in his hand as he walks over to his cabinet to get a drink. When he opens the cabinet, the cane is nowhere in sight. After Bullseye spears Kingpin's olive with a pencil, the cane is magically back in his hand.
In the church fight between Daredevil and Bullseye, Daredevil throws his cane/stick at Bullseye, the camera then cuts back to Daredevil who is running towards Bullseye and his cane is back in his hand (the one he threw), then he picks his cane up from the floor, yet is seen only carrying the one he just picked up.
(at around 1h 35 mins) When Urich finishes his article exposing Murdock as Daredevil he decides to delete it. He presses the delete key but the computer begins backspacing.
(at around 1h 22 mins) Bullseye uses an organ pipe as a club to fight Daredevil. Metal organ pipes are typically made of thinly rolled lead or a lead and tin alloy. If one could manage to lift and swing the heavy pipe, the soft metal would collapse in the hands before even the first blow could be landed.
(at around 27 mins) The burning 'DD' reflected in Ben Urich's glasses is the right way round, when it should be mirror imaged.
(at around 20 mins) After Quesada's trial, Matt and Froggy are upset that "another scumbag rapist" was going free. This would seem to indicate a criminal proceeding. If that's so, they would not be prosecuting the case. A district attorney would. Conversely if the trial is civil (as it appears to be since the victim is at the table with the lawyers) then the outcome of the trial would have no bearing on whether Quesada went free or not.
When young Matt wakes up in the hospital room after the blinding accident, the first item he senses is very obviously an IV drip. After being frightened by other sounds, he falls off the bed, and crawls away from it, to the corner of the room; he is clearly NOT hooked to the IV. It'd be pointless for an IV to be started without connecting it to the patient.
In all her battles, Elektra uses her sais in a very incorrect manner. She has her fingers in between the prongs, which eliminates the sai's primary purpose, which is to trap an opponent's weapon. The way she holds her sais actually puts her fingers in danger. Plus, the sais are blunt weapons, not sharp.
(at around 1h 21 mins) During the battle in the church, Daredevil and Bullseye dangle from a horizontal organ pipe. Such an organ pipe is very carefully balanced in the vertical position secured by only one small hook mounted on a wall bracket. Should that hook come undone, the organ pipe would fall to the ground immediately.
(at around 9 mins) When young Matt awakes in hospital after his original chemical accident, the vital medical equipment is not connected to him.
(at around 12 mins) When young Daredevil slides down the railing, wires are visible for a fraction of a second.
Wires lifting up Elektra during the rooftop battle.
(at around 1h 10 mins) When Bullseye says to Kingpin "I want a bloody costume", the background behind him changes. Also, he's clearly saying the original "I want a fucking costume" line, put back into the director's cut DVD.
When they are at the party at the fictional "Grand Hotel" in Manhattan, we can clearly see the lobby of the Los Angeles Biltmore hotel in the background. The Los Angeles Biltmore just happens to be located on a street called "Grand Avenue".
Foggy hands Matt the mustard instead of the honey, but he should that Matt would know the difference in the shape of the two containers.
(at around 12 mins) Daredevil refers to his vision as "a kind of radar sense", but the images he perceives are created by sound waves, not radio waves, so it would actually be a kind of sonar sense.