Similar/related topic links.

As your website gets bigger you can post links on the bottom of your page to similar topics that are already on your website, this is good for larger websites such as forums.

1. It gives you more internal links

2. Provides the user with information they are likely to be interested in, so they will surf longer.

Linking to useful websites with authority in your area, such as wilkipedia, will give you more credibility, opposed to linking to websites with no authority. I will often link to useful websites to show that I am credible.