Subreddit communities. Particularly the small to mid-size ones. I honestly think knowing how to use subreddits as a resource is essential to being a functional user of the Internet. It's a crowd-curated feed of all things relevant to any particular topic, presented in a way that is consistent and meaningful.
For example, I'm debating between Android and iPhone for my next upgrade. I really only want to use iOS if it's jailbroken. So what's the latest jailbreak news? There are probably some forums or tech blog primers that could give me the answers I need, but the easiest way to get that info, is to go to r/jailbreak. Chances are, the sidebar will have everything I need.
You want to get your dad a nice shaving kit for father's day? r/wicked_edge. Interested in owning a noisy keyboard? r/mechanicalkeyboards. Why doesn't the guy next to you wash his jeans? r/rawdenim. Just experience your first panic attack? r/anxiety. What are the essential hip-hop albums I should listen to? r/hiphopheads. Classical? r/classicalmusic. Jazz? You guessed it, r/jazz.
There are thousands of medium-sized subreddits that cater specifically to one thing, and the content of those subreddits has all been curated, critiqued, and discussed by an organic, self-motivated user base. I may only be interested in the subject-matter for a short time and narrow purpose, but the community of that subreddit is interested in that subject-matter all the time, and they've done all the leg-work for me. I know the information I get will have undergone more review and rigor than almost any other source on the Internet. As a bonus, the organization of that information is always presented in the same familiar way, so I don't have to learn a new UI or workflow.
And that's just for using subreddits as one-time information repositories. You've also got the power of reddit as a newsfeed. Again, I can follow a subreddit for daily updates on whatever topic I want. This is so incredibly advantageous to those following sports, TV shows, or news events. ESPN is fine if I want general sports news, but what if I only want news about my local NFL team (the Seahawks)? I could follow a Seahawks blog, but then that's just a few people generating content. Instead, I can go to r/seahawks. There I've got all the content distilled, updated, and sorted for me: blogs, Twitter posts, articles from beat journalists, plus all the user discussion in response to this content.