In another thread someone brought up the nuisance of someone linking to a bad URL on your site, linking to a non-existent web page. The 404 error log is a great place to find those kinds of bad inbound links and have the site publisher correct them. However if you can't correct the link then rewrite the URL to the best page. Don't waste it on an error page. That's a poor experience for the site visitor, it's bad for the link juice to waste it on a 404 page when it could be directed to the intended target of the link.
Another way to recover a link is to track down dead end pages and add a link back to the home page. Typical dead end pages are PDFs and other document files.
If your site is popular then typos on links and direct navigation traffic are inevitable. Think in terms of plurals and singulars, with or without certain words in front of your actual domain name, reversal of words in your domain name, even tld and cctld variants. Redirect all of those to the actual site to recover bad links and mistyped direct navigation.
What are other ways that you know of for taking advantage of latent link opportunities?