I see someone already listed a bunch of hexbear comms, maybe as a half joke, but seriously some of them are the most active and fun if you're a lefty. But a couple non-hexbear comms worth suggesting are

!piracy@lemmy.dbzer0.com
&
!privacy@lemmy.ml

Perhaps also !memes@lemmy.ml if you want not just leftist memes but also the drama of indignant, sometimes enraged libs (even an occassional frothing chud) coming into the comments and usually proving the accuracy of the meme they're upset about. It's one of the best comms for that reason.

If you want great news analysis I would also suggest not just a news comm, but more specifically the newsmega thread at hexbear. It will change url every week since its a single post thread, not a comm. But it stands on its own so well I think its worth mentioning along with entire comms or instances. Hexbear has a certain reputation, some of it deserved (much of it not), but the bulletins and international news thread (aka newsmega) is, regardless of what you may think of the rest of the instance, one of the best places on the internet to get serious leftist/anti-imperialist analysis of current news and events as far as short form "reddit-like" (I hate to phrase it that way but you know what I mean) commentary and discussion.