The Nostalgia Critic sounds incredibly girly when he screams. Which is often. In a commentary, he said he does this intentionally because it's funnier than if he screams normally which just makes him sound angry.
The Spoony One does this repeatedly when he sees the cover of the Wing Commander movie. He also does an excellent one when he finds out that the Critic is reviewing The Room. He also goes up a couple octaves in surprise and/or insane frustration during the course of Ultima VIII.
Youtube duo Crazy Commentaries has both of the members (but mostly Jay) doing this on occasion.
PyschadelicSnake is the KING of this trope when it comes to horror Let's Plays. Go ahead, pick any video from a horror game he's played and I guarantee he'll scream at least once. His latest vids has the tail end of him finishing Ju-On The Grudge on the Wii, and he screams every minute.
YouTube user HamsterAlliance has given many examples of this, shrieking and yelling in surprise when he gets close to dying in a game or something scary happens unexpectedly.
Like PsychadelicSnake and HamsterAlliance, PewDiePie is also very notable for his incredibly girlish screams. Especially in his earlier playthroughs. He even points out how girly his screams are. A lot of the time, he ends up in tears after a huge scare. Either that or he's in KittenTherapy.