Reddit, for starters. There are a lot of great sub-Reddits you can subscribe to and you can remove a lot of the pointless default ones (/r/atheism, /r/politics, /r/aww, etc.) so you end up with a feed that really suits you.
http://inbound.org/ is basically HN for people also interested in online marketing, SEO, etc - lots of great practical stuff ends up on there that never makes HN.
I use Flipboard to aggregate the best stories from several sources. They have a heap of design feeds already listed as well as business, tech and HN in there too. Best part is its easy to flick quickly through headlines, share what you want and also save to instapaper for later.
1. Quora - To participate in discussions and learn new things
2. http://zenhabits.net - Minimalism and Better habits
4. Techcrunch, GigaOm, Engadget - Tech Trends
5. Fubiz.net - For daily dose of inspirations
I used to keep up with tens of blogs and sites via RSS, as I got busier it became obvious I couldn't possibly keep up with all of them. Now HN & NYTimes is the only place I visit and occasionally Lifehacker. HN filters out most of what I don't care about.