Steph: I'd be fucking stoked if they weren't releasing me today!
Marble Hornets has one early on that does a good job at setting the mood: "Burn them."
For the first dozen or so videos, J was strictly a narrator and viewpoint character. After a while, he started to get a bit more involved, visiting locations and interviewing witnesses to try and piece together the mystery. Then, in 19, things happened. "I have been recording myself for a month now..."
"Season 2", like the first part, opens with Entry 27's Wham Line. "The past 7 months are completely missing from my memory."
"There is something bothering me. I don't remember any of this happening".
Entry #49: "I told you not to follow me!"
Entry #64: It's been over a year since Alex has made his presence known, some presumed him dead. When Jay and Tim go explore the tunnel in Rosswood, Jay's phone rings.
Phone: Leave. Now.
Jay: That was Alex!
Vampire Quest: "When I was a child...I...was kidnapped...by Lilicore as retribution."
Achyls: "Blow the collar! I said BLOW THE FUCKING COLLAR!"
Sparky: "It-it...it won't work, Sir!"
The final line of V3 is a massive example.
B58 - Johnathan Rizzolo - Deceased
"An attempt was made by a military organization to rescue some of the contestants in this season of Survival of the Fittest. The lives of many students were lost as a result of the actions of your governments. Any future attempts will be met with an immediate and total detonation of all collars."
This later turns out to be a rare subversion in the form of a Red Herring; it turns out that all the v4 escapees are alive and well.
In Perfect Kirby 3, Kirby tells Roy he knows about the Hippin' Jippin' Gene.
Cecil: This is Cecil, and I do not know where I am. It is clearly a radio studio, but the walls are covered in blood, and instead of dials and buttons on the soundboard, there is just animal viscera, glistening under the green LED lights.
Episode 32, Yellow Helicopters, gives us two in the space of about a minute and a half.
...the witnesses said that some low-flying yellow helicopters began dropping orange leaflets onto the city streets. The leaflets read, "StrexCorp Synernists Inc. Look around you. Strex. Look inside you. Strex. Go to sleep. Strex. Believe in a smiling god. StrexCorp: It is everything."
''Oh! Oh no. Uh... dear listeners, we must issue an apology! Those helicopters are completely... safe. Even safer than safe! In fact, StrexCorp recently bought our little radio station from the mysterious unseen forces who founded it centuries ago!
Before all of those:
Cecil: Old Woman Josie says that the Angels who have been living with her ... helping around the house and ultimately protecting her from all evils ... have disappeared.
They've really been upping the ante recently. Episode 33 gives us:
Cecil: I...I don't remember having a brother.
Episode 47 opens with a Wham Line that will have many saying "Oh shit":
Welcome... to the Greater Desert Bluffs Metropolitan Area.
The SCP Foundation has several of these. Often an entry will lead the reader in a certain direction by deliberately not revealing all of the object's qualities; the Wham Line will then drastically change the tone of the piece. Particularly good ones are for SCP-1025, SCP-804, SCP-089, and SCP-093's associated entries.
SCP-089: "For each locution event, SCP-089-A is a healthy, unblemished human infant or child between eight months and six years of age, and SCP-089-B is that child's natural mother."
SCP-093: there was no war it was him him him him him IT. IT. it came from between the folds of time and space and worlds and light and dark something that is but should not be slipped in and called out to them as their god and they believed it and they tasted it and touched it and layed with it and became its property and did its will and IT IS STILL HERE
SCP-1000: "They're smarter - to be precise, they are exactly as smart as us."
SCP-2000, being a bit of a Wham SCP, has several, but three in particular stand out:
"Object Class: Thaumiel"
"Previous attempts to ameliorate violent and sociopathic tendencies in humanity as a whole have already been implemented and deemed successful."
"Valid Foundation security credentials for Dr. Alto Clef were discovered nearby, although a genetic match could not be established"
—->"Object Class: Thaumiel" by itself is a Wham Line since that object class, while not restricted per se, is something that no-one can mess with and keep their article on the site unless it's very good. Only a handful of such articles exist.
—->"Object Class: Apollyon" is an even more rare example.
SCP-2317: Special Containment Procedures: Irrelevant.
-In it...is everything. So many aspects of what just happened in this entire fiasco of a "competition". The Meteor. The device to stop it. The things found in Big Mt. The state of the wasteland itself. The hiring of individuals from other worlds to eliminate political enemies on this one. All cobbled together from sections of a very ancient and much bigger plan by a "Courier Six"...to eliminate anyone who would oppose his rule of New Vegas-
The Angry Video Game Nerd: At the climax of the Desert Bus episode, where the Nerd has just made a suddenrealization that after ten years, his work on warning people about shitty games is failing. He tops it all with four jarring words.