I'm surprised no one has mentioned this but a really good option is Prismatic (getprismatic.com). You basically just follow topics/sites and it suggests to you

I'm surprised no one has mentioned this but a really good option is Prismatic (getprismatic.com). You basically just follow topics/sites and it suggests to you more sites/topics which are similar. Browsing from there I get all the big articles on hacker news and from other sources which I wasn't aware of previously.