Most webmasters do link to useful articles and resources on other sites. That is a best practice on the Internet. Besides, the more you link to others, the more likely it is that others will link to your great content. Of course, just because you are linking to other sites does not mean you should not change the attributes and the behavior of your links. WP External Links is a powerful plugin that lets you modify the behavior of your outgoing links.
WP External Links puts you in control of your external links. You can define how they will be opened and whether they will be a follow or nofollow link (hint: you don’t want all your link to be nofollow). This plugin allows you to pick and choose which links you want affected.
Want to make your internal links and external links look different? You can modify the look of your external links under Style Settings section. If you know your way around CSS, you can customize the look and feel of your links further.
If you want to nofollow all your external links or give them a different look from your internal links, WP Internal Links has you covered.