One of these is not often cited, but still something you should focus on - particularly if you have a blog. And that is that Google takes into account the quality and relevance of the sites that you link to.
In short, if you are citing quality articles and blog posts that are relevant to the point that you are making then it will reflect well back on your own blog. That's why I would suggest searching the news aggregators often - Google News being the biggest and best.
This will this bring you the most authoritative sites - with the big companies like CNN and News Ltd having high page rank, usually 6 or above. These sites are also really stable and enduring, which is important. Even if the article or blog post in question gets removed and you end linking to a blank page, the main URL will still be there.
Smaller sites and blogs, however, are often being run by individuals in their spare time and sometimes end up going belly up. The domains get picked up and used by other webmasters - some of them building gambling and sex sites. It's possible that if you do a lot of linking out to such blogs, you could eventually end up linking to a "bad neighborhood" without knowing it, and subsequently be penalized.