The Ring/WMG

Samara didn't record her videotape over a football game at the cabin.
It's too convoluted; how did she get the power to tape over things in progress? There's a much simpler explanation which makes much more sense: Cole Sear helped her record the tape in an effort to help her pass on. Poor optimistic kid...

Samara is not a ghost; she's an alien of the same species as "The Wire" from Doctor Who.
Both exist as images on TV screens; both are able to stretch out from the screen and attack people, leaving their faces deformed. Alternately, The Wire and Samara are the same entity; the Doctor forgot to tape over the video which he trapped her on, and it found its way into the cabin. Having been imprisoned on the tape for so long, the Wire has gone mad and all that's left of its mind are the disconnected and nasty images on the Curse Tape, as well as a psychotic desire to destroy humans.

There being more than one Wire would also explain why the events in The Ring occurred in both Japan and the USA.


 * The Wire was originally trapped on a Betamax tape (presumably as a failsafe measure) but it's entirely possible that the Doctor automatically transferred his Betamax tapes to VHS without watching each one to make sure it wasn't imprisoning an evil entity. We've all done that at least once.

Samara DOESN'T require people to copy the tape to lift the curse
Samara spared Rachel because she found her dead body, and her son because he's another child (or just to thank Rachel). Noah dies because he never entered the well and Samara didn't notice that he helped out too.
 * This, however, doesn't explain all the survivors from Samara's cult in the 'rings' mini-story.
 * Their deaths mean nothing to Samara?

Samara's powers come from electromagnetism.
Notice how all the things she levitates with her mind have some metal in them. She created a partial backup of her mind by magnetically rearranging a videotape. The people she's marked for death show up fuzzy on video cameras because her magnetic powers interfere with their electronics. It has also been established that particularly strong EM waves can effect the brain; this is how she kills, by projecting powerful EM waves at some key part of the victim's brain, causing it to fail catastrophically. Note this only applies to the American version. Sadako does a few things that can't be explained this way, such as predicting the future & communicating with smallpox.

The events of the Ring movies happened inside a computer simulation; Samara is a virus
This is actually the premise of Loop, the third novel of the Japanese Ringu series. In this novel, set in the "real" world, a computer simulation called "Loop" exists, and that is where the events of the previous two novels ("Ringu" and "Rasen") took place, and where Samara (Sadako) is nothing but a computer virus. The novel also explains that Noah (or better, his Japanese equivalent) realizes that he is living in a simulation, and uses his phone to contact the lab in the real world where the simulation is being run, asking the scientist who answers to "bring him to wherever he is". The scientists synthesize human DNA to reproduce the virtual "Noah" exactly and create the main character of the novel. Unbeknownst to them, when "Noah" made the call, he was already infected by Samara (Sadako), who changed his DNA, so they also brought her in the real world, as a real virus.
 * On that note, am I the only one that thinks said main characters father was the "outside force" that also fathered Sadako?

Andou is really Koji Suzuki
In Rasen, Andou makes a deal with Sadako, and writes a book about what happened, which acts as a vehicle for the virus. Obviously, this was the novel 'Ringu', and Koji is merley claiming it as fiction to cast disbelief. This also means Rie Inou is Sadako, as the book ends with Sadako auditioning for and being cast as the role of Sadako in the movie being made based on his book. THE TRUTH IS OUT THERE PEOPLE!
 * Additionally, Loop is an attempt to further discredit it by saying it was all a simulation anyway.
 * or else that we ARE in the Matrix

There is no Samara. The film has an overcranked version of the Videodrome signal in it.
The signal is adjusted improperly, so instead of predisposing people who watch the video towards violence and making them suggestible, it gives them severe radiation poisoning. All of the strange things they see as they slowly die are taken from their subconscious, having been planted there by the video. The phone call occurs because they've all heard the Urban Legend about the phone call, and are already hallucinating.

Samara was possessed as a baby.
It's strongly implied that Evelyn (Samara's biological mother) is a psychic: she knows when people are going to come for help, could see that Samara was ... er, Samara, etc. It could be possible that Samara was one as well, making her susceptible to possession when she was too young to fight it off. Poor Samara was forced to "sleep" her entire life as an evil spirit destroyed the life she could have had.

Samara has been rendered powerless due to advances in technology.
Samara seems to be an Invincible Villain and Karma Houdini, but one theory claims otherwise. She is nearly unstoppable and should you watch her tape, the only way to save yourself is to copy the tape and send it to someone else; the idea being that the recipient would watch the tape and become her next victim. But what would happen if the recipient simply had no VCR? Such devices have become obsolete since the last entry of the original franchise, and VCR tapes are very hard to copy onto DVD or BlueRay. It stands to reason that eventually, Samara would become trapped, with nobody able to watch her tape due to lack of anything to play it on.