Enter PostRank:

http://www.postrank.com/feed/

For every RSS feed you will get 4 RSS sub-feeds:

1. Best posts.

2. Great posts.

3. Good posts.

4. All posts.

The ranking (to decide if a post is good/great/best) is done through its popularity online (reddit, digg, delicious, etc.).

When I'm interested in a website I usually subscribe to the best posts sub-feed, sometimes to the great posts sub-feed. This way I'm never overloaded with RSS items to read and I don't miss anything important.

Here are ultra-filtered HN sub-feeds using a feed of HN posts of 150 votes or above:

http://www.postrank.com/feed/20ad1f84cfa8acedf528c616cd441f6...

Also, here is a JavaScript bookmarklet I created to find the PostRank sub-feeds for the current website you're on:

  javascript:location.href='http://page2rss.com/page?url=+encodeURIComponent(location.href);

EDIT: ReFilter is also very useful if you want to only read posts about a particular topic:

http://re.rephrase.net/filter/