24/WMG

The cougar was a part of the nuclear conspiracy all along.
Otherwise, the events surrounding Kim Bauer in season two have no relevance to the rest of the plot. Besides, the cougar's timing of showing up just when Kim is out of danger seems highly suspicious. It's likely that the cougar was recruited to keep tabs on Kim in case she would be needed to control Jack Bauer later in the day.

By the time her cover was broken, Nina Myers had shifted her loyalty to Jack and CTU.
Upon re-watching season one, it becomes clear that Nina missed numerous opportunities -- every opportunity -- to impede Jack in his investigation of and thwarting of the Drazens, whom she supposedly works for. She could easily have passed information to them that would have helped them without blowing her cover. Her relationship with Jack doesn't appear to have had any strategic benefit for her -- and since Teri Bauer could tell Nina had been seeing Jack (and wasn't over him) from one look on Nina's face at a time when Nina would not have been feigning feelings for Jack, those feelings must have been genuine. The only instances we know of her working against CTU is when she kills Jamey, which was necessary to maintain her cover, and when she tells the Drazens that Palmer's still alive, which she didn't do immediately after finding out - which she should and could have done; instead, she waited until after she learned that Teri Bauer was pregnant. Perhaps she did it in a fit of irrational jealousy. Until then, she had thoroughly become the mask.
 * And then she kills Teri for absolutely no reason. Uh... hang on...
 * Repeat: irrational jealousy. She was Yandere enough to think Jack would go for her if she murdered the hypotenuse in the Jack-Teri-Nina love triangle.

The events have all been controlled by an unknown Kira.
The CTU is a wing of the SPK set up to locate and capture this Kira. Jack Bauer was hired as the only man tough enough to shrug off a Death Note. Or perhaps he's destined to die already...
 * Well, he's died twice now. If anything can take him...

The Big Bad of the final "day" will be...Jack Bauer.
Think about it. He was under tremendous psychological strain the first time around, and it's been getting worse every single season. His patent pending Jack Bauer Interrogation Technique already puts him on the slippery slope with his knees bent. Jack finally snapping and taking it out on America as only Jack Bauer could almost seems like the only satisfying way to end the show.
 * So, the final episode is Bauer making the entire Earth explode.
 * So Jack would have to be stopped by Agent Walker?
 * What a delicious theory! No, he'll be stopped by the other Agent Walker and.....a reformed Tony Almeida.
 * He'd need some real confidence shakers to break his trust in America to do that.
 * You mean everything thus far isn't enough?

Wayne Palmer is brain dead.
The swearing-in for Allison Taylor in the movie Redemption did not have any former Presidents visibly present (which would be a near-impossibility in real life); but the fact that the almost immediate former President Palmer is entirely, completely absent from the picture implies that he is in such a physical condition that he could not attend the ceremony in any way - maybe attached to an iron lung. Why not dead? Word of God has said he is "somewhere" in the world of 24.

Jacks granddaughter will get kidnapped or used against him in the next season.
She is Kim's daughter.

Marwan was actually aiming at Shelbyville with that nuclear missile in season 4.
Now we know what day that Simpsons crossover took place.

In the last hour of Season 8 Jack will perform Heroic Sacrifice and die.
Cause if this is really Bauer's last day, this is how writers should end it - of course if they keep their tradition of Bittersweet Ending. Of course this Troper will be more that happy to find out that he is wrong and Jack and Renee will live Happily Ever After. But does it really sounds like something in show's style? No.
 * Then who will be in The Movie?
 * Jack Bauer, of course. It's going to be a Prequel to the entire series.

Tony's back.
Now there is only one way how we can see Tony again. He must be in prison now. So somewhere in the middle of the season it will be revealed that while working with terrorists for 3 years he got information or, more likely, some connections, which he can use to help Jack now. There is also a very big chance Tony will die trying to help because Redemption Equals Death and Anyone Can Die (not to mention Bittersweet Ending). Poor Tony.

Every single person who's ever been affiliated with the CTU is secretly working for someone else.
Behind the scenes are various groups with their own interests that are waging a secret war with each other. They use the CTU as a way of keeping track of their enemies' agents. The reason why whoever does the screening lets these people in is because they are part of a secret conspiracy that's been manipulating every single organization involved. The reason torture under Jack Bauer works is because the true mastermind has been convincing various terrorist groups (probably truthfully) that Jack Bauer is one of the people who are ultimately in charge of everything.

Jack Bauer goes to the bathroom during the commercial breaks
I don't care how Badass you are. No one can hold it for twenty-four hours.
 * There were actually plans to show Jack coming out of a restroom after a commercial break, but it was scrapped.

Wayne Palmer was a Republican, and by extention, Alison Taylor was a Democrat.
We know from Day 1, that David Palmer was a Democrat. And his opponent during the Presidential elction in season 3, John Keeler, is logicaly a Republican (or at least some fictional party that is similar to the Republican party), as was his Vice President that became President, Charles Logan and his V.P Hal Gardner. During Day 6 Wayne Palmer is President. Now logically you would assume he'd be a Democrat like his brother was. But I'm not so sure. See, after the evnts of Day 5, the Republican party was thrown into chaos, given that in one term they went through 3 different Presidents. So Tom Lennox, a major figure in the party, got with Wayne Palmer and asked him to run for the Republicans. Now, it's not unlikely that Wayne was already a registered Repbublican when he was his brothers Chief of Staff. After David Palmer sacked Mike Novik, he wanted someone who he knew would be loyal to him (as Novik conspired to remove him from office), but would also offer constructive criticism to any of his decisons. His brother Wayne being a member of the rival party, could always give him the other sides point of view objectivly on any issue, but would always be loyal to David because he is his Brother. So Wayne Palmer ran for the Republican party, he was a risky choice as he had limited experience, but he still won both the primary's and the general election for a number of reasons. A) He is the Brother of seemingly one of the most popular presidents in recent History. B) His experience in politics may be limited but it was as the Chief of Staff, which has to count for a lot! C) Given that the Republicans went through 3 presidents in 1 term, its likely that the Democrats choose a safe, but weak candidate as they thought the election would be a breeze. It wasnt, and Wayne Palmer won by a nosehair. However, after Wayne was incapacitated, the public had finally given up with the republican party, and given that the Democrats choose Alison Taylor, the first Female Presidential candidate, Daniels got absolutley destroyed in the election.

Max and/or Trepkos are members of Wilson's group.
If there's any way to tie most of the series together, this could be the best way to do it.

Jack Bauer is a Super Soldier.
Come on, how else would Jack be such a crazy-arsed bad ass like he is?

Josh is Jack's son.
It's not really that wild if one thinks about it. Jack and Marilyn had a relationship prior to her marriage to Graem, so who's to say she didn't sleep with Jack, get pregnant, and then claim it was Graem's kid? And to be honest, the way they chose actors made Josh look a lot more like Jack's kid than Graem's. Also, according to the executive producer of the show, even the writers think that Josh is Jack's son.

The real mole is the one of CTU's human resources people.
How else can there be so many moles in CTU?