Not sure if all of these would classify as BigYouTubers, in no perticular order :
PewDiePie - Yeah, most of the time he's annoying and seems as he's trying too hard, but some of his LP's are awesome, especially when he genuinely enjoys the game he's playing (Fahrenheit, for the best recent example)
Ashens - The man's just so naturaly funny and could probably do reviews of anything in the world and make it funny.
The Amazing Atheist - TJ sometimes rants on about stuff he's ranted about for a million times, but more often than not he's very interesting and thought provoking
A Dose Of Buckley - although he can be a bit douchey and elitist (without realizing it, apparently), runs a very fun show to watch
TheRadBrad - He sucks at most games I've seen him play, but is such a positive character that I stick to his LP's and get frustrated and yell at the screen, and ultimately get enjoyment out of it - it's very weird...
Kikoskia - One of the best and most dedicated LPers out there, while being naturaly funny and making even the boring grinding and leveling in old-school RPG's fun to watch.
TotalBiscuit - WTF is... ? series are awesome, but I like the commentary given in Content Patch even more.
NonStampCollector - a very cool and funny atheist cartoonist
potholer54 - the best dismantler of YEC's nonsense in the world
jonlajoie - although not as active on the channel in the last months, the man's a bloody genious
Retsuprae - well, the true LP celebrities, what can I say more ?
lophatjello - aka Happy Video Game Nerd, very cool retro reviews
Also should mention the guys I originally saw on YT, but then went on to watch on their sites :
AVGN, Spoony, SideScrollers, AngryJoe, Pat the NES Punk, The Cinema Snob...