S4 is imminent so here's a S3 YTP compilation to celebrate. Like the S1-S2 one this was for personal use but I figured I'd put it up. Again, it's 99% other people's work. Sources below.

The first ~10 minutes is a grab bag, the rest goes in approximate episode order except for Spike at Your Service because I'm stupid and lumped all the Spike stuff together.

http://www.youtube.com/user/MLPoopCollections
Is a great source of MLP YTPs, especially finding below the radar poopers.

SOURCES

Maple Pony and PikalaxALT deserve a lot more subs! Check them out.

http://www.youtube.com/user/themaplepony
Cadence Is Fine
Camping is Horrible
Magic Mare Duel
Pinkie Games (Collab Entry)
Pony Fragments
The Wing Trap
Wonderbolt Catastrophe

http://www.youtube.com/user/PikalaxALT
Alex Trebek tracks a winter storm to a mare's campsite
Dimly-lit Shimmer files a complaint against Viacom
Fear does not a stallion make
Fuschia Flambee Finds Fun Frolicking Far From Filly Fields
Vegas was simply unable to avoid crashing

http://www.youtube.com/user/Alfonzopancakes
Demonic Pinkie Pie

http://www.youtube.com/user/Znuffle
Alexander doesn't even like pasta.
We bought a great dane Mr. Spider Vagina
Derpy is a nuke
Glaze puts up a music force field
Hole Wreck Academy for Assholes
Nicey fapt seed
One bad Applejack
Scootaloo hates Rainbowdash flavored chicken wings
MUF!

http://www.youtube.com/user/Siwwous
The Apple Family Reunion is a Disaster

http://www.youtube.com/user/PonyRedundantMare
Faps Seed
Pinkie Pinkie Redundant Pie

http://www.youtube.com/user/Mrrpivots
Cosmic Friendship Device

http://www.youtube.com/user/jesse2282
Angel the Bunny is a Total Douchebag (REMOVED from youtube)
Shining Armor Will Fart On Your Crystal Cock

http://www.youtube.com/user/Haloya101
Spike becomes Applejack's sex slave

http://www.youtube.com/user/IAmInHurt
A Luna Matata
Spike the Bad Dragon
Spike's Harmful Addiction
Twilight Resurrects a Demon
Double Snowpoop
Spike is replaced by a living tombstone

http://www.youtube.com/user/AverageJoeCinema
YTP - Woods Goods
Discord's House of Memes
Jack and the Crystal Empire

http://www.youtube.com/user/Grobisam
My Friendly Friends_Friends are Friends : The Crystal Censorship

http://www.youtube.com/user/Dipy7878i
Poor Little Pony Scootabuse was Magic
My Major Musical Mysterious Moving Motions
The poop that's not a poop
YTP: Greetings Soophie - Google Chrom
My Evil Pony AppleBloom discovers true Friendship

http://www.youtube.com/user/Popplebanger
Lucky Luke and the Phallus of Time

http://www.youtube.com/user/GayRainbowDash
Princess Celestia and the quest for a good laxative
Applejack has a dead granny
Twilight Sparkle explodes
Snowdrop gives snot to the princesses

http://www.youtube.com/user/HareDoctor
Crystal Empire Part 2 in a Nutshell

http://www.youtube.com/user/olibacon
Friendship is Fabulous II Smagic Shmuel

http://www.youtube.com/user/Acoustic1234567
(YTP) Mah Lil' Pygmee: Friendship is Sweaty Socks in a Steamy Shower With Two Pieces of Garlic
removed?

http://www.youtube.com/user/DaThings1
The Ground Roundup

http://www.youtube.com/user/MrSpiderVagina
We bought a great dane
Dainishe cookie watches Little Pony Shop

http://www.youtube.com/user/madasylum1
Cole Belle's Lament
The Equestrian-Dixie Crusade

Sire
http://www.youtube.com/user/xPrEpWnEdx
The Babyspitter Regurgitates Some Horriterrifying Jokes and Hypnotises People with Bacon
A Sphere Emergency Strikes the Town of Hollybo

http://www.youtube.com/user/OpusMaGinty
YTP Juice IV: The Goblet of FJJJJJJJJJ

http://www.youtube.com/user/ThatsWhatUCallClass
Short Sliding Sponges Spilling Salty Stillbirths

http://www.youtube.com/user/ChiefDoggingfood
Snowdrop has impeccable taste

http://www.youtube.com/user/ManMonocle
Pony is Pony: Crystal Empire State of Mind [Collab Entry]

http://www.youtube.com/user/LifeMakesMeLOL
Magical Mystery Shit.wmv

http://www.youtube.com/user/Bombinmepants
Discord summons sanity and order to Equestria

http://www.youtube.com/user/MrNinjapony
My Little Pony with CENSOR BLEEPS! part 3: games ponies play

http://www.youtube.com/user/Danfango700
God Burns Down Equestria for Insurance Money Danfango.avi

http://www.youtube.com/user/LimeyLassen
Howdy Doo!
Pyynkh'Omegna

http://www.youtube.com/user/FitzCharisma
Mulp Fimtion - My Little Good Life

http://www.youtube.com/user/MrCurrentlyUnknown
Seeing Rainbows Ass puts everypony in a good mood

marshmallow:
Simpsons Did It, Trixie

http://www.youtube.com/user/2007excalibur2007
Worth the weight.

http://www.youtube.com/user/AustRock9080
Pinkie Pie Premature Porn Star

PaleoSteno
https://www.youtube.com/user/PaleoSteno
Hey Lauren Faust, how should My Little Pony: Friendship Is Magic end? (original vid missing/deleted)

https://www.youtube.com/user/TrixieReturns/featured
HELICOPTER B*TCH

Unknown sources and/or dead accounts:

Babs Becomes An Hero

Smashing Pinkie Pie Nigel face