The Old Guys
Courtney Campbell - still runs 'Hack and Slash' which had a big impact on the culture. Is still posting but at a reduced volume. Courtney, if you want me to move you out of the 'Old Guys' then let me know.
James Maliszewski - ran Grognardia, a fundamental OSR blog, currently doing a Tekumel fanzine.
Jeff Rients - ran a central gaming blog, recently released Broodmother Sky Fortress through LotFP.
Justin Alexander - from the Alexandrian blog has a following I know nothing about. (Checks,.. holy shit his Patreon gets $108.00 per post.)
See Stuart Whites comment for a list of other important influences.
Drangonsfoot - A forum of the true old Gygaxian Grognards. Had a big influence on the early OSR and still chugging along. Total membership is just over 10,000.
odd74 - I know very little about these guys, they seem similar to Dragonsfoot to me. Currently at just over 2000 members. (Described as 'chill, drama free, dull and specialised')
Knights-n-Knaves - Similar to the above, currently at just over 1000 total members.
rpg.net - almost all of the people that I personally know, don't use rpg.net or use it minimally. It's almost a defining element for my immediate social circle and even many of the Big Personalities above who hate each other can still agree that they hate rpg.net more. I know Kevin Crawford is still on there a bit.
Lamentations Of The Flame Princess
North Wind Adventures
See Christopher Richardsons comment below for a deeper look into this.