The 5th Cylon is Newt, from Aliens

It's a good thing that the BSG crew and Cylons landed during the day, because Rebecca 'Newt' Jorden (she goes by Newt and only her brother can call her Rebecca) usually goes into hiding at night. And why is that? Because "they mostly come at night ... mostly." In this case, the "they" would be humans and Cylons, not acid-for-blood aliens.

Why it works:
The ultimate goal for a Cylon is to become more human-like. For the final Cylon model to be a scared little girl hiding from an alien menace, I think I would at least call them a friend long enough for them to show me how to navigate the complex maze of air ducts to escape the creatures. Resurrection Ship be damned, Newt would show the other Cylons what it truly means to survive and fear death. Plus, she's overly attached to a doll head, which goes a lot farther than the usual infatuation with human/Cylon babies or just one of the humans in general.

Oh, but there's more! She chooses a surrogate mother. She mocks soldiers. She screams. AND she sometimes wears a helmet that's too big for her. Have you EVER seen another Cylon do that kind of stuff? Of course you haven't, that's why Newt would fool the hell out of you.

Why it doesn’t work:
An Aliens-BSG crossover isn't quite what the fans have in mind for any type of explanation. Additionally, introducing another species/evil entity into the mix wouldn't help wrap up the series in 10 episodes. And lastly, the chick who played Newt is like super-old now, she wouldn't fit into the same small spaces that the Newt circa-Aliens could.

Odds that I’m right:
1977:1

The 5th Cylon is Jennifer Lopez as Selena

Crazier things have happened. Sorta. Here’s how it shakes down: Just like it happened here on Earth, on Aquaria, J-Lo as Selena is murdered by her fan club manager. The only difference is that she was brought back to life by her manager/battlestar commander/secret adoptive father, Bill Adama. She goes into seclusion to recover from the almost-fatal gunshot wound only to emerge years later on one of the many starships in the fleet as the final Cylon.

Why it works:
Selena’s great. She’s funny, smart, cute and has musical talent. Besides, we’d all love to watch J-Lo as Selena the Cylon on Battlestar, wouldn’t we? Six would get all jealous and Baltar would start seeing J-Lo in his head all the time instead of Caprica-Six. Does J-Lo as Selena the Cylon’s spine glow red when she gets worked up, sexually? I can guarantee a bunch of you would watch to find out. If it’s all about ratings and money, this might be a good call.

And, come to think of it, we’ve never really met a musically inclined Cylon, have we? Could J-Lo as Selena the Cylon be responsible for having created the music that the previous four Cylons(Tigh, Anders, Foster & Tyrol) heard and drew them together? Maybe?

Finally, who among us hasn't been looking forward to seeing Edward James Olmos and J-Lo together again on-screen? For some reason their stars just shine brighter when they're together.

Why it doesn’t work:
Not a clue. Seems like J-Lo as Selena the Cylon would be a perfect fit for the 5th Cylon. Duh.

Odds that I’m right:
2261:3

The 5th Cylon is Scott Bakula

Since this is science fiction, they got the Quantum Leap and Star Trekking part right. But, "putting right what once went wrong?" Frak that. This time Scott Bakula is back with a skinjob vengeance -- putting humans in cages that once went free. He'd probably do some freaky science experiments on them, too.

Why it works:
The chemistry between Bakula and Dean Stockwell is reason enough for this to make sense. They could be the Cylon version of Butch Cassidy and the Sundance Kid. Riding around Earth, looting desolate cities and hijacking derailed train cars. They won't be miffed by some silly bicycle metaphor, though, because they ARE the future. Well, not really, since the resurrection ship has been destroyed. But Bakula could be that one Cylon that seems evil, only to save face at the end of the series and ensure the human way of life. He's just charismatic enough to pull it off.

Why it doesn't work:
The television public couldn't handle a Quantum Leap reunion. Nor could one actor grace the cast of three popular science fiction shows and live to tell about it. Then there's the fact that he's never been in an episode yet and there's no room for anyone that has a random white patch of hair on their head -- Cylons are nearly perfect (ahem, I said nearly... looking at Cylon Pirate Tigh).

Odds that I'm right:
521:1

The 5th Cylon is Zak Adama

Thowing us a massive curve ball, we come to find that the final Cylon is none other than Admiral Adama’s dead son, Zak Adama. Didn’t see that one coming, did you?

Why it works:
Zak Adama is dead, dude. Remember how Starbuck cleared him to fly even though he was a crap pilot... and then he died? How could he be the final Cylon? Well, Cylons have the ability to “resurrect,” right? Maybe after he was killed in that training exercise, he was resurrected on a nearby Cylon resurrection ship. Since then he’s been partying in secret with the sixes on some private basestar, just living the dream, man; Hot chicks, blow, connect four. If this turns out to be the case, it’s going to be a major mindfrak for Admiral Adama, Starbuck and Lee Adama… and would make for some really interesting storylines in the last half of the season. You gotta admit, it’s certainly an interesting possibility.

Plus, we could add one to the list of Cylons that Starbuck has fraked. I’m betting that by the end of the season, she’ll have totally gotten it on with a Centurian.

Why is doesn’t work:
Really? His dead son comes back to life only to be revealed as a Cylon? There are so many other viable, more believable and straight-up better options for the final Cylon model. While it could make for some interesting TV, it just seems too far-fetched. Basically, they’d really be pulling one out of their asses for this to happen.

Odds that I'm right:
310:1

The 5th Cylon is Adama's Geiger Counter

When we last saw Adama, he was toiling around with dirt on Earth. More specifically, he was measuring the amount of radiation on the ocean shore (which will probably put a big damper on that Colonial Fleet-wide beach party they were planning). But who's to say that Adama wasn't tricked ... by the final Cylon!

Why it works:
As we've stated before, Cylons are machines. If you're unawares, geiger counters are machines, too. And what have the Cylons wanted to do since day one? No, not blow up the 12 colonies (which they pretty much did). They wanted to find Earth (which is ironic since five of them have already been there -- why not just go there in the first place?). So now that they've found Earth, the ol' hidden Cylon makes his/her appearance and tells the humans that it's WAY too dangerous to stay there. Radiation kills humans dead. Not robots. Plus, we're familiar with the geiger counter -- it's been in the fleet since day one and they've probably sniffed out a few bombs with it here and there.

Why it doesn't work:
A gods damned geiger counter? Yeah, absolutely ridiculous. Those things have about as much personality as two Number Fours. Besides, we'd all have to learn an intricate series of clicks as its language, unless they translate what it says for us across the bottom as it speaks. No one is overly thrilled with that idea, though.

Odds that I'm right:
1,000:1

The 5th Cylon is Kevin Sorbo

I can see it now: Pulling a “Lost,” the creative folks at BSG decide to introduce a new character that’s supposedly always been there, but for some reason has never been seen by us the viewer. Somehow, Mechanic # 7 becomes a central character and, to the delight of geeks everywhere, it turns out to be none other than Kevin Sorbo.

Why it works:
We already know Xena (aka #3, aka D’Anna Diers) is a Cylon, so why not Hercules? He’s on record saying that he “would love to do it” which is no surprise seeing as that he’s made a career working in the sci-fi and fantasy genres. Not only does he have an interest, but Sorbo has also worked with BSG Executive Producer David Eick on the Hercules series so the connections are already in place. Plus, with all the references to Greek mythology, it only follows that the son of Zeus would play a part in the BSG universe, right?

Why it doesn’t work:
C’Mon, Hercules as the fifth Cylon? Let’s get real. It might as well be The Highlander (There can be only one… final Cylon) or The Renegade Lorenzo Lamas or some other ridiculous character from a show you used to watch on USA after school all those years ago. Also, the final Cylon is supposed to be a character we’re already familiar with. So why would the big revelation of the last Cylon be some low level mechanic, or some other minor character that we’ve never seen before who is also Kevin Sorbo? Pretty sure we’d of spotted him at some point over the last three and a half seasons. Maybe he was in a coma?

Odds that I’m right:
850:1

The 5th Cylon is Jake

Imagine waking up to the feeling of someone, or something licking your toes. Sounds like something a dog would do, yeah? Well what if I told you that "dog" was really a Cylon!?! What in the Gods!?! Today we explore how Jake the dog (with the yellow bowl) could be the 5th Cylon.

Why it works:
It's perfect, 3 out of the 4 revealed Cylons were on New Caprica and a part of the resistance. Jake was totally there, too, and his yellow dog bowl was a signal for passing information back and forth. Jake could have known everything the humans were doing. Additionally, Jake didn't care whether he was sniffing/licking humans or Cylons. And as we've known, Cylons are apt to take on human lovers -- which feeds the notion that a dog is a man's best friend. Oh the irony!

Why it doesn't work:
The last Cylon is a dog? How could the Cylons follow a dog as a leader? I can see it now, in the throws of an intense battle over radioactive dirt on Earth, Jake must stop giving orders only to scratch behind his ear, lick his balls and hump the leg of Leoben (it's always funnier if it's a dude). I'm sure there's also an episode where Jake blames the pile of crap on the baseship on Six.

Odds that I'm right:
400:1