How do you not know about them!! Do you even have the the internet!!!!! Bro do you even game!!!!!!
Well the WGC is a huge group on youtube with many players and artist from around the world and some big names in the UK most of the worlds golden demons are dominated by people from this group or friends of..
The main hub channel is War Games Consortium.
http://www.youtube.com/user/WGConsortium/aboutThe channels I watch mostly out of the 23 listed are
awesomepaintjob
http://www.youtube.com/user/awesomepaintjobLester has lots of useful tip for people using airbrushes and the over all video quality is superb IMO the best paining tutorial set up on the tubes.
Worthy Painting
http://www.youtube.com/user/WorthyPAINTING ichibanpainting
http://www.youtube.com/user/ichibanpainting Hugo is a top painter and covers more than just GW lots of x-wing repaints have been appearing of late. As well as some really good tutorials on how to make good youtube vids.
TemplarsCrusade01
http://www.youtube.com/user/TemplarsCrusade01 A UK based player with lean towards quick and dirty paint for huge campaigns and pre-heresy goodness he's just started to branch out of more than 40k. An excellent entertainer.
A few people I also watch are
Cuffy
http://www.youtube.com/user/Chuffy1976Nice vids a little bit on the comic book style when his work is finished but superbly done.
Buypainted
http://www.youtube.com/user/BuypaintedA good selection of content with some very nicely done stuff.
Jawaballs
http://www.youtube.com/user/jawaballsA bit of a joke at times was huge in the community but lost respect awhile back with other members and is a bit of a fringe element these days most useful for beginners and wannabe Tourny players his bet reps and tutorial are a bit all over the place.
ScaleModelMedic
http://www.youtube.com/user/ScaleModelMedicNothing this guy does is in a hurry but he takes detailing to a whole other level!
Terranscapes
http://www.youtube.com/user/Terranscapes Mike is the boss when it come to terrain and product reviews and testing. His vids ara little long but well worth it.
VaultsOfTerra
http://www.youtube.com/user/VaultsOfTerra Lots of background and lore vids good for a listen in the background of a painting session.
I do watch more people than this many more! Most of these people do both battle reports as well as painting videos. Have a look some you might like other not so much but consider it home work and a good insight to what the rest of the community are doing on youtube.