In this post Matt Cutts from MattCutts.com (and Google) shares what he did in 2007 that improved his blog the most.
The shortest, easiest thing I started doing was using linkify.
You just highlight some text and click the bookmarklet to open Google’s search results. Pick the result you wanted and click “create link” and the hyperlink is pasted into your text form.
Since I’ve been using linkify, I’ve found that I link out to good sites more often.