Hello DW, long time no see! I've been wanting to do this challenge but Day 1 wasn't for me so I'm starting with Day 2:

In your own space, promote three communities, challenges, blogs, pages, Twitters, Tumblrs or platforms and explain why you love them.

I'm making three themes instead of three discrete recs:

Podfic
I've got to say that podfic fandom is super organized and full of neat resources, challenges and communities, like podfic which retweets conversations and questions about podfic and keep you up to speed. Podfic fandom is even doing it's exchanges on twitter, see ITPE_mod . Then there's podfic_tips wich is still active and actually helpful and the newly-minted podfic_love , for recs. Or if youwant to practice your French or are francophone, there's franco_podfic . I think everybody already knows the audiofic archive but I'll still link it, just in case! A labor of love and it shows :)

Last, one challenge I definitely want to do one day is pod_together because I love fandom best when it fosters exchange and collaboration between fans with different passions and skillsets. 

Fandom
metanews  / metanewsfandom - I've been keeping up with this still relatively young community and while the majority of the links aren'tt really of interest to me I do occasionally find some thought-provoking meta. I really like that this exists and hope that the pool of submitters will get larger in time.

fail_fandomanon - Is this really a community to rec? Well, it's definitely an acquired taste and a lot of the repetitive wanking can be frustrating and tedious. But then you can get all the recs and make threads about whatever you like to chat about and get discussion - and you have all the lovely bitter ex-OTW nonnies, the nonnies who can agree that yes, the racist fic really is racist and the nonnies who agree that BBP looks shady as fuck and you feel like you might actually need FFA in your fandom life to keep your faith. The opportunity to host non-hierarchical exchange (in a space without internet dudebros) is something I really value about the journaling services with their threaded comments. 

Art&Education (these are totally fandoms!)
felixdeon - this dude's stock is a goldmine when you like drawing men and slash, so I keep returning to it. I especially like that he offers so many ~artistic poses, a good variety of poses and angles and multiple figures interacting. The only downside is that bodytypes are rather limited. 
I really like the metmuseum youtube channel which features documentaries and lectures and recently a fun little web series with info-bites about select pieces.
Just recently I also found the YaleCourses channel which features some select lectures which have been made accessible and so far I've been really enjoying this Introduction to the Old Testament. Watching Christine Haynes fangirl the bible is a joy, I like the structuring and how clearly she articulates her points and draws her distinctions.