mitcho (Michael Yoshitaka Erlewine)

Sometimes you have a need for having links to external URLs show up interspersed among your own pages or posts. This plugin lets you easily create such “redirecting” posts or pages by simply setting a custom field.
Usage: Add the custom field with label “redirect” to any post or page. Enter the redirect target URL as the value of that custom field. Now all links on your site to that post or page will be replaced with that redirect URL! If you try to visit the permalink URL for that page, it will redirect the user to that redirect URL too.
This plugin actually also works fine to redirect a URL to another URL on the same site as well.
Placeholders: New in version 0.9: the strings <code>%home%</code> and <code>%site%</code> in URLs are replaced by the WordPress home URL and site URLs, respectively.
Development of this plugin was supported by the <a href="http://arts.mit.edu/" rel="nofollow ugc">Arts at MIT</a>.

Redirect by Custom Field

Changes the URLs pointing to pages and posts which have a "redirect" custom field, using that entry as the URL instead.

peterarends

Redirects you to the proper URL of the website. In case of stumbling upon a working alias.
Normally (depending on your settings or control panel) http://misterwebsite.nl (an alias of www.mrwebsite.nl) just works, but it should be redirected to <a href="http://www.mrwebsite.nl" title="MrWebsite" rel="nofollow ugc">http://www.mrwebsite.nl</a>. 
The same goes for http://mrwebsite.nl (it should be with www. instead without), https://www.mrwebsite.nl (it should be http instead of https) and all other aliases.
Before WordPress 3 this just worked out of the box. But it does not anymore.

Proper Redirect

Redirects you to the proper URL of the website. In case of stumbling upon a working alias.

Redirect by Custom Field vs Proper Redirect