OK, so I've never been so addicted to someone that I watch EVERY SINGLE VIDEO THEY'VE EVER MADE, but I do have some Youtubers that I just can't get enough of.
1. Tobuscus
Ah, Toby Turner. He never fails to make me smile. Whether it's a ridiculous song parody
(haha I don't know how to make the cool words-that-link-to-videos like you guys do so you'll have to find one on your own :3), a ridiculous ORIGINAL song, a ridiculous literal trailer song...everything he does is just ridiculous. And since I'm ridiculous, it's my kind of humor. :3
2. PewDiePie
Pewds~...no favorite Youtuber list would be complete without at least one Bro. That's right, I am a Bro. PewDiePie's ridiculously funny. All of his Let's Plays make me laugh, even when the game is supposed to be terrifying/really dramatic, like Amnesia or Heavy Rain. If he didn't curse so much, he'd probably be, like, my top favorite Youtuber. As it is, I still love watching him.
3. Jessica Nash or [Razzy] The Musical Lyricist
Well, I'm a sucker for Vocaloid songs. Jessica Nash, otherwise known as Miku-tan (it is her, I swear it), is an English cover artist who covers songs from Vocaloid and other popular franchises. Razzy is also an English cover artist who uploads some of Miku-tan's covers himself and sings quite wonderfully, if not almost over-the-top sometimes.
It's awesome when they sing together, like when Miku-tan provided the voice for Miku in Razzy's cover of The Madness of Duke Venomania (extra points to Robert, the voice of Kaito in that song, too) or when Miku-tan and Razzy joined with Shiroko, another cover artist, to sing Choose Me. WHEE~. It's beautiful.
Honestly, Jessica Nash/Miku-tan is so incredibly good at singing, I want her to become a professional. I suggest her Egoselfish cover, it's impeccable.
I've found that Jessica Nash and I sing very similar in terms of style. We both have pretty thick voices, go into our head voices easily, scoop notes often, and as evidenced by her World is Mine cover, when we're supposed to be saying something in a song that sounds cute, we tend to speak in a really cute voice and try to make ourselves sounds cuter than we really are

That doesn't mean my voice is like hers. I just WISH it were. XD
4. WatchMojo.com
OK, I don't know if these guys even count, but they make Top Ten lists, and I really love watching them. Maybe it's just because I like lists. But they always give an interesting commentary, and occasional clips from the media in question helps. That, and the fact that they made a Top Ten voice acting in video games list, and Joel and Ellie from The Last of Us were included.
So, yeah. That's pretty much it.