Depends a lot on your interests! Some good ones I've aggregated over the years:

• Pluralistic by Cory Doctorow: Daily links for reading by a very pro-decentralization and free web person
• A Collection of Unmitigated Pedantry: History and Pop Culture, usually one post per week on Friday
• Pedestrian Observations: Public transportation and urban design
• People's Policy Project: RSS feed for articles from the only crowd funded think tank (Lefty if you're interested)
• Bartosz Ciechanowski: Great blog with interesting animations, all very well researched. Only downside is that you usually have to use the RSS feed as a method of knowing when the article is posted and following the link to the website, plus he usually only posts one every 3 months or so
• xkcd: Old guard web comics, always fun to read

There are a lot of great RSS feeds out there though! I encourage you to see if your favorite blogs or news sites or things like that also have RSS feeds and suggest consuming them on there (for example I read CBC and Radio Canada exclusively through RSS) as it usually streamlines the whole reading experience.

If you use Apple's Ecosystem, I would also suggest using MacStories' Find RSS Feed Shortcut which will grab any available feeds from any website you feed it and let you copy the link to your clipboard to add to your favorite app. Enjoy!