SIMNoFollow

Add rel="nofollow"
Adding rel="nofollow" to your outgoing links is a well-known method to improve your website's SEO by reducing leakage.

Add target="blank"
While adding target="blank" to your outgoing links will not improve your website's SEO (search engines ignore this attribute), it's a good idea because it retains your users' focus, instead of losing them to external sites.

Add External Link icon
Add an icon at the end of your outgoing links so that your users won't be "surprised" when clicking on something opens up a new tab. This is to improve the general user experience, and SIMNoFollow is the only plugin of its kind with this feature.