Takes place in an alternate universe where Celestia and Luna used the Elements of Harmony to slay King Sombra.

Celestia and Luna are no more. The sun and moon have collided, and the heavens torn asunder in the aftermath of their final battle. The Elements of Harmony are missing, presumed forever lost. The fiends of Tartarus are on a rampage, and no one can stop them. And to make things perfect, the ruler of the nation of Boardor has decided to invade.
Desperate, Clover the Clever's last living student gathers together 108 virgin mares, in order to perform a ritual that will revive King Sombra. They succeed... kinda.
A human, in King Sombra's body, suddenly finds himself in an Equestria in a downward spiral with a bunch of technicolor ponies begging him to save them. Convinced that he's either dreaming, stoned, or insane, he tries to go along with it as best he can, although the voice in his head, a very angry voice with a hunger for conquest, crystals, slavery, and stairs, isn't doing much to instill confidence in his own sanity...

New Cover Art By Shadow Bolt!

After a tragic accident, a human ends up in Lord Tirek's body, as part of an attempt to reform the villain after his recent escapades. While the hero of our tale is trying to make sense of his new surroundings, the rest of Equestria thinks that the most terrible threat that their world has ever seen is back...
And the powers that be are definitely not happy about it.
New Cover Art By Shadow Bolt

TL;DR - Blueblood is a gritty alicorn superhero.

The coronation of Princess Twilight Sparkle… Blueblood can’t stand it! Somepony gets a pair of wings and suddenly they become royalty and the talk of Equestria! It’s just not fair!

When a mysterious guest offers him wings of his own and even more newfound abilities, how could Blueblood possibly refuse? The power is everything he’d ever dreamed of.

But when Blueblood discovers that he’s not the only pony in Canterlot with a mysterious benefactor granting them special gifts, he realizes that something nefarious is going on. Now, with his most bitter rival as his unwilling ally, Equestria’s most unpopular royal is going to have to find it within himself to be the hero Equestria doesn’t want, but definitely needs.

Cowritten by RainbowBob

Celestia has a dangerous creature held in the deepest of Canterlot's high-security dungeons. It can create ponies (with full backgrounds and histories) with it's strange and often-times prophetic powers. The Princess does her best to keep it under wraps, but its only a matter of time before it's "creativity" will get out of control.

Pinkie takes the day off work. Spike loses his cupcakes. Twilight is disappointed in Spike's knowledge of history. Bulbasaur just wants ponies to recognize him for who he is.

Applejack thinks she's having a bad hair day. Her friends, however, think it's something else.

Guest Krillin: Zero Man

Now with sequel!

An accident in the lab sends our favorite boy genius to Equestria, as a pony. What will he do and how will he get back? The answer: Science! (Cover Art Updated!)
New FAQ! and TV Tropes!
Planned Phrases from Dexter:
“Pinkie Pie! Don’t push that Button!” /to Pinkie
“Please, Magic is the word simpletons and the ignorant use to describe what they cannot understand.”/ to Twilight
“No, I didn't strap a rocket to you. I strapped you to a rocket.” /to Rainbow Dash
“Friends? Who needs friends?”

Dexter is a boy super-genius with a disdain for anything girlish and no desire for friendship. After an mishap in his lab, he gets stuck in Equestria. How will he cope with the over-friendly ponies, and the girlish everything?
For any who do not know Dexter's Lab: http://en.wikipedia.org/wiki/Dexter's_Laboratory
[RIP Christine Cavanaugh: 8/16/63-12/22/2014] - Dexter's Original Voice Actress

At her coronation after-party, Twilight gets a little freaked out at the prospect of growing into her new life, especially one specific aspect of it. She knows better than anyone that talking her problems over with a friend can help tremendously, but she doesn't have many friends with whom she'd be comfortable talking about this particular problem, let alone ones who would really understand what she's going through.

...unless she broadens her definition of "friend."

Now with a reading, courtesy of PresentPerfect! Go check it out, if you're so inclined.
Ahora en español gracias al maravilloso trabajo de SPANIARD KIWI!
(Now in Spanish thanks to the brilliant work of SPANIARD KIWI!)

A secret unknown to any hornless pony, unicorn horns are made of candy. Pinkie Pie found out, and now she wants to try every flavor!

Warning: contains awkward moments and far too much non-consensual horn licking. Proceed at the risk of your horn and your dignity.

Available in Chinese, courtesy of Hell Organist.
Available in Russian, courtesy of boatOV.
Audio Reading by CaptainBron3y.
Second Audio Reading by Kanjigirl.
Featured on Equestria Daily.

Based on this story:
Pegasus Wings Are Made Of Ice Cream
The Taste Of Madness
Lyra's Candy Shoppe
Candy Is Made Of Unicorn Horns
How Many Licks?
To Prevent Horn Decay
Unicorn Horns Are Made of Heroin
Over His Dead Body
A Luscious Loophole
Dr. Doofenshirtz's Sweet Revenge
That Thing We Do
#DealWithIt
Unicorn Horns are...
Unicorn Horns Are Loaded With Calories
Charlie The Unicorn's Horn Is Made Of Candy

Due to a typo on her permit to build a new barn, and the meddling of a recalcitrant bureaucrat, Applejack is stuck running a bar, at least until Mayor Mare gets back to town. So sit down and have a drink in Ponyville's least likely watering hole!