The fabled 'bunny' who appears silhouetted in a scene in season 1 appears many times, according to this interview with Elisha Cuthbert: http://www.homunculus.com/articles/cuthbertelisha/cuthbertfhm0210.html

Reiko Aylesworth auditioned for Nina Myers, but lost to Sarah Clarke. When Joel Surnow and Robert Cochran were casting the second season, they remembered her and cast her as Michelle Dessler.

Co-creators Joel Surnow and Robert Cochran have admitted to naming characters after tennis and chess players respectively, while producer Michael Loceff names characters after people from Foothill College, where he teaches. Submitted by Dandude

Over the course of each season, Sterling Rush (head of the props department) takes an average of 10 to 12 thousand photos of sets, props and characters, in order to ensure continuity between scenes and episodes. Submitted by Dandude

The main character of the show was originally going to be named Jack Barrett. The creators of the show decided they didn't like the name, and changed it to "Bauer" after Elaine Bauer, an executive at Imagine Entertainment. Submitted by Dandude

Co-creator Joel Surnow originally named Carlos Bernard's character "Tonio" Almeida, but Kiefer Sutherland was unable to say this name and ended up calling him "Tony" instead. Submitted by Dandude

Each member of the cast of 24 is required to trim their hair every 5 days.

Glenn Morshower who plays Aaron Pierce is the only actor besides Sutherland to appear in all six seasons. Submitted by Ictoabu

Reiko Aylesworth based her performance as Michelle Dessler on her mother. Submitted by Cubs Fan

In the final episode of the first series, when Nina is erasing information from the computer, all the pictures you can see on the screen are of the cast and crew. One of these pictures features Kiefer Sutherland kissing a small cuddly toy.

To ensure that the season 1 finale wasn't given away by anyone, a number of different final episodes were filmed.

Lou Diamond Phillips made two appearances on the show, as Mark DeSalvo, the security chief where Victor Drazen is being held. Philips and star Kiefer Sutherland are known for having worked together in the two "Young Guns" films.

This is a very strange observation that I made of the scene where George enters Jack's office as he's changing. Just after George says he's in charge, Jack jokingly says, "So they thought you'd do a better job keeping an eye on me than Alberta would." Just at that moment, he kicks a shoebox out of his way, and the sound it makes sounds exactly like a rimshot of a drum, unintentionally making a mockery of the joke he just made.

Alberta Green, who makes her first appearance in this episode, was named for actress Alberta Watson, whom series creator Joel Surnow originally wanted to play the role. Ironically, Watson played Erin Driscoll, a character that is by-the-book, much like Green is, in Season 4.

Eric Balfour began a series of guest appearances as Milo Pressman; the name was also used in the film Stand By Me, in which star Kiefer Sutherland appeared as a small-town bully.

While filming the first series of 24, the terrorist attacks of September 11th occurred. This is why the plane explosion is rarely mentioned as the series goes on.

Sarah Clarke was cast as Nina Myers the morning filming for the pilot was to begin; the costume department didn't have time to fit her, so she wore her own clothes during the season

During production, Dennis Haysbert was shuttling back and forth between Los Angeles and the East coast, because he was filming "Far From Heaven" at the same time.

Both Sarah Clarke and Xander Berkeley have played turncoat government agents assisting terrorists attempting to assassinate the President. Clarke on 24, and Berkeley in the film Air Force One, when the President interferes with the terrorists' insidious plan. Ironically, the pair began dating during season one, and by season two, they were married.

We get the impression from the first few episodes that Nina is trustworthy only to find out in the last 2 episodes that she was the main mole inside CTU. It's funny though that it was in front of our eyes the whole time, by accident or design: Every time that Jack says his famous starting monologue,when he comes to the part "...and people I work with might be involved in both..." we see Jack looking at Nina.