https://www.fanfiction.net/s/8405328/1/The-Town-That-Time-Forgot

Perfect little one-shot. Honestly, the first time I read it, it scared me. It's darker than anything the show's ever done, and unnervingly plausible to boot. And those last few lines... damn, just... check it out. It's amazing.

I personally like eternalyouth from Xiaolin Showdown.
Hivefled from Homestuck is good, but it has some hiccups here and there.
And the Pony Pov Series has an special ´lace in my heart.
Finally, i really like The darkness series (Descent into the darkness and the breeding darkness) from harry potter.

https://www.fanfiction.net/s/5630547/1/What-the-Sorting-Hat-Said

From Terminator Fanfiction, I present Terminator 3 A New Life. It's about the Skynet Program, who managed to send itself back in the timeline of Terminator: Sarah Connor Chronicles. It takes its own interpretation of the world of Terminator and reapplies it to the plot of T:SCC. It deviates a bit far from T:SCC while making it a rough guideline, but expands the Terminator world even more.

https://www.fanfiction.net/s/4045203/1/Terminator-3-A-New-Life

I have no idea what do you think of Dakari-King Mykan, but I find his self-inserts rather entertaining. He does manage to make himself relevant to the world he fits himself in, but he also didn't take the spotlight most of the time. I present one example of his work.

https://www.fanfiction.net/s/8577926/1/7teen-Jude-for-Prime-Minister

I have no idea why I like this story. I leave it to those knowledgeable of Silmarillion to judge my taste.

https://www.fanfiction.net/s/8886314/1/Oh-These-Saturdays

Among the MLP fandom (as several others have turned to for their recommendations), my love goes out to these two fics especially, due to their hilarious deconstruction of common Mary Sue tropes (and the latter being one of the reasons that I know of the PPC besides).

Outside of the bronydom, there's also this​ Frozen/Tangled crossover. These are two continua that are known to have coexisted, and this fic explores that with everyone in character. And it's amazing.

Can be found right here. I also enjoy "Past Sins" by PenstrokePony, RealityCheck's "Nyxverse" (both on fimfiction), and "A Storm of Chaos" by Shotoman (Doctor Who crossover).

If you're not really into ponies, you can read Karalora's "Crowns of the Kingdom", which is about Disneyland. :)

And that would be Fallout: Equestria, one of the most well known MLP fanfics. I adore this fic. I love the characters, I love the themes it explores, I love the setting, I love everything about this fic. I have talked extensively about this fic before on this very board, but I will gladly plug it again.

Now, some warnings. This is My Little Pony crossed with Fallout. You do not need knowledge of the Fallout universe. In fact, it's probably better if you do not know the Fallout setting. Trust me, when I first read it, I had never played a Fallout game, and I still loved it. That said, this is also a mature rated fic, for very good reason. There are drugs, violence, swearing, and heavy sexual themes. This is not a light and fluffy story (though there are some lighter moments.) If you do not like dark stories, especially when put in Equestria, then this fic is not for you. If you are easily disturbed, this fic is probably not for you. A good test is this: can you make it through Ponyville? If yes, strap in, you are in for an amazing ride. If not, fine. Just hop off there, and feel no shame for not liking it.

https://www.fanfiction.net/s/10360620/1/A-Guide-to-Your-Life-Under-Lord-Sauron

This is a pretty funny one-shit from the LOTR archive.

This is my second real interaction here, and I must say, it was a good one. Thanks for all the fic!

The are of course OFUM, Suedom and HFA. Suedom was actually the first fanfic I ever read. Which probably explains a lot now that I think about it.

But setting these well known works aside, my favourite is A Bed of Thorns by Nym. Warning, NSFW, contains tastefully naughty bits. http://archiveofourown.org/works/377718/ It's a Once Upon a Time fic, set in an AU where Rumpelstiltskin married Belle and where Storybrook never happened. (I think. It's still a work in progress.)
Its focus is mostly on character and relationship development. Also, it is a prime example of how good erotica can be when it's written by someone who actually knows how anatomy works.

And then there's my rec list: http://ppc.wikia.com/wiki/PPCRecCenter/EileenAlphabet%27s_List

iheartmwpp's Just Another Harry Potter Movie Parody series. Absolutely hysterical. Her book parodies are also pretty great.

Also Reverse by Lady Moonglow: Excellent AU Dramione, where Hermione ends up in a parallel world where everything's reversed- the good guys are bad, the bad guys are good, Lily Evans is alive and terrifying to cross, Dumbledore's an evil overlord, Tom Riddle is a loving father, and Purebloods are tortured and kept as slaves. It's fairly grimdark and graphic, but so well-written!

Then there's Against the Moon by Stoplight Delight. It's a great account of the Marauders' days at Hogwarts. At times hilarious and heartbreaking. Plus the author knows it ought to be set in the seventies, and makes references appropriately. We loves it, precious.

(My friends and I love Thirty Hs, it's hillaribad.)

I think it will be Arctic Rim. Why? Dunno, maybe because it was the first one I ever read.

Game Theory and its sequel Power Games are the bestest things ever.