Ghost Whisperer/WMG

"Wide-Brim" and the Sinister Man from Xkcd are the same person.
They're certainly both evil enough, for starters. It would also explain where Mr. Romano has been all this time. And with xkcd's sparse level of detail, you can't be sure that the Sinister Man doesn't look and act like a cross between Freddy Krueger and Truman Capote.
 * Romano might not be evil enough. Sure, he seemed that way at first, but then we found out with the air hostess that the people he convinces can come back and cross over if it turns out they don't like being with him. Is a Deal With the Devil supposed to be "satisfaction guaranteed"?

Ghosts are attracted to Melinda Gordon's cleavage.
Hey, if it worked for Jennifer Love Hewitt's career...
 * And it worked on the male audience.
 * Actually in a non joking sense it does make a lot of sense. The entire series has appeared (especially more so in its later seasons) to seem like a Americanized Live Action version of many formulaic paranormal themed anime and manga Fan Service series (and for a while the show was actually adapted into a Comic and manga series where Melinda's clothes (or lack of them) was more noticeable).

Also the series up to a point seemed to follow the trope of Beauty Equals Goodness, anyway ghosts really do seem to be more attracted to Melinda and appear to seem more willing to open up to her because of this. Basically it goes like this. Adult Male ghosts come (no pun intended) to her specifically because shes hot and because she can see them they some of them may believe they have a chance of being able to "Physically" do other things with her if you catch my drift. Child ghosts (especially male children) feel more comfortable around her and feel less threatened. And some of the female ghosts may have some subtle form of Les Yay towards Melinda going on.

Add in to this the fact that regardless of the fact that Melinda's husband is a firefighter (in a small town that seems to rarely have any fires) is rarely shown (allowing her more solo shots in the majority of the show) and Many of the female supporting characters on the show that believe and help in Melinda's powers also are at various levels of genuine attractiveness and wear some skin bearing clothing as well. All this gives the appearance that Ghost Whisperer (which oddly enough is co-created, written, and produced by a Male Psychic apparently from his point of view) takes place in a universe of Sexy Psychic Female Witches some who help people in little ways (talk to the dead) to save the world on a regular basis. This all leads to this theory...

Ghost Whisperer and Charmed exist in the same universe
Think about it the ladies of the 2 shows do seem thematically similar also Sabrina the Teenage Witch COULD be thrown in there as well.

The Gaussian Girl-style ghosts at Melinda and Jim/Sam's wedding are those she's crossed over
Either they got a "day pass" to say congratulations or it's their good feelings in physical (ectoplasmic? magnetic force field?) form.
 * They're the "Shineys" that only Aidan can see, but exactly what they are hasn't been confirmed.
 * They have been in the season 5 finale.

Medium is going to be after Ghost Whisperer on Fridays. You know what that means -
Wacky Crossover time! Hilarity will ensue when Allison keeps seeing Sam/Jim as some weird double-exposure man while Melinda has to deal with her Enfant Terrible messing with the three Du Boise girls.
 * Derp! Guess who just canceled! GW MAY cross over to ABC.
 * Even if the show wasn't canceled a crossover would have been doubtful mainly because the 2 shows were too different in themes and emotional tone. while GW is more fairly light hearted (Melinda mainly saw only non criminal ghosts who needed help with a final goodbye to loved ones). Medium was far too dark and grimmer by comparison (Allison mainly saw ghosts of psychotic serial killers and rapists in nightmarish dreams and even when their not Dark Knight style criminals even the spirits of supposedly sane people were somewhat of a Jerkass to her because apparently somehow almost everyone winds up in Hell.).
 * Heck just the above reason is enough for the "dream" pairing of these 2 shows never too meet because just the mere meeting of the 2 women would almost instantly come to blows after Allison learns that while she has lived nearly her entire life with psychosis inducing literally physically jarring visions every night Melinda had only mildly frightening visions (while awake) and has almost saintly accepted her defacto role as The Chosen One of her palatial little town (by comparison Real Life Arizona is not the most fun place to be in the summer).
 * Finally add in the fact that the combined shows Sliding scales of cynicism would eventually crash and die a fiery death (Melinda wanting to believe that some of the ghosts can be redeemed (with her Sexy magic no doubt! this however seems to have actually happened in some GW episodes) with Allison in an almost vigilante rant (partially due to some resentment towards Melinda) wants her counterpart to banish em' all ta' Hades and let God sort em' out.)

The Shadows and Shineys are Dementors and (weak, sapient) Patronii.
While not as solid as Dementors, the Shadows are wispy, turn out lights, and cause people to remember their worst memories due to being made of people's worst memories; the less-seen Shineys are wholly good but curiously weak against the Shadows.
 * Jossed, at least for Shinies/Shineys/however the hell it's spelled. The final episode

Melinda can't really see ghosts.
Her Grandma was lying to her about her schitzophrenia. Melina is schitzo and is slowly getting other people to believe in her delusions. She spies on people and learns intimate details. Then she imagines these details as the ghost of someone recently deceased. She's trying to be Dr. Phil and help people.

Melinda's breasts are enchanted.
Think about it. It explains why no one calls the police while she runs around and harasses people. How Melinda's antique store stays in business (people can't collect her debts because they can't look directly at her). The show isn't exploiting her breasts: her breasts are a major plot point!
 * This also coincides with the theory above also meets as a Sexy case of Can't Get in Trouble For Nuthin'

Melinda is a prostitute.
Her antique store is just a front. This explains why she never gets any business and can afford to keep it shut half the time: Melinda is turning tricks behind the store. She NEEDS to wear those revealing clothes: it's a business expense

Melinds is a witch/sorceress/genie,etc and is PRETENDING to be a "Ghost Whisperer."
1) Her husband went from being a firefighter to being a doctor in less than 5 years. 2) Her son aged from an infant to 5-6 years old in less than 3 years. 3) She manages to keep an antique business open despite spending almost no time at the store. 4) She's never sued,imprisoned nor even seriously injured despite numerous adventures that would have lead to those outcomes. 5) All of her "whisperings" end on a mostly positive note w/ the ghosts leaving (e.g. No "stalker" ghosts)and all of the people involved mostly happy w/ the outcomes.

How are all these things possible unless Melinda possess a magical ability (or abilities) that she chooses to manifest as "ghost whispering?"