Ok, lets see shall we...
Pyrocynical - My favourite YouTuber at the moment. He is similar to Leafyishere, but without the annoying voice, douchy attitude, and rabid fans. He is funny as fuck, and his reaction videos are great. He also seems like a genuinely nice guy.
Filthy Frank - Papa Franku's videos are so, well... bizzare, but hilarious at the same time. You'd be surprised that underneath all this NSFW weirdness there is actually a very interesting plot and lore to his videos. The characters are also very interesting. Like Chin-Chin, for example.
IdubzzzTV - Funny guy who I first discovered while watching Filthy Frank videos. I especially love is Content Cop and Kickstarter Crap series.
H3H3 - Ethan and Hila are awesome! I love them for their great reaction videos and skits. Vape Nation is my personal favourite video of theirs.
JonTron - This guy is absolutely hilarious. Like, sometimes I laugh so hard watching his videos that I actually start crying. His reactions are just priceless, as is some of the stuff he says. I love all of his videos, but ones I really enjoy in particular are his Bootleg game reviews, and his reviews on crappy movies (his review on 'A Talking Cat!?!' for example).
Top5s - I often binge-watch his videos, because I honestly think they are really well made, and interesting of course. I really love his videos on creepy stuff such as; conspiracy theories, ghosts, and strange stuff on the internet. He also does cool short documentaries on stuff as well.
Cr1tikal/penguinz0 - Without a doubt one of the funniest game commentators on YouTube. I love his dry sense of humour and 'no fucks given' attitude. He really makes me crack up when, instead of running away from the monsters in horror games, he insults them while chasing after them. Most other YouTubers would scream and run, but nope, not this guy.
Mr.Nightmare - 90% of the stuff I watch on YouTube is on creepy subjects (ghosts for example), so I really enjoy his videos. Like Top5s, I just find his stuff interesting.
TheBooReview - Two guys that review videos of ghosts and other unexplained phenomena that their fans suggest, usually crappy/hilarious videos and obvious fakes that they tear to bits. They usually have a monthly video roundup, which in my opinion are their best videos. The videos they have been uploading lately have been a bit 'meh', but hopefully that will change because I really like these guys.
EDIT: Thankfully they have been uploading some great content lately, and I actually marathoned all their vids yesterday. The Boo Review is saved, and I love their channel even more now!
I Hate Everything - Does videos on things he hates, and they are hilarious. I love his 'Search for the Worst' series were he reviews crappy movies.
Shane Dawson - A lot of people hate on Shane because his humour can be a bit, well, disgusting at times, but I honestly find him really funny despite it. I love his Conspiracy Theory videos, and his videos were he tries different things (weird kids toys, weird food, 99cent store items, etc). His DIY videos are pretty funny as well, especially the ones were he 'galaxy-fies' stuff.
Ashens - A funny guy who reviews strange things, including bootleg toys, items from 'poundland', and fake phones and video game consoles. He also does food specials, where he often eats disgustingly out-of-date food (20+ year-old baby food, for example).
Chadtronic - Another commentator that often reviews strange, obsure internet videos. He also reviews games, weird toys, and strange commercials. I find his content to be very entertaining.
Honourable Mentions: Game Grumps, jacksepticeye (I used to hate on this guy because I thought he was loud and obnoxious like PewDiePie and Markiplier, but I gave him a chance and I actually enjoy his content, and how excited he gets over playing some games. He can be loud and over the top sometimes, but I don't mind), Dan and Phil, The Nostalgia Critic, Lazy Masquerade.