Beej

In WordPress, attachments default to having their own pages. Sometimes, 
this is not desirable, as in search engine results. Use this small plugin to 
redirect your attachment pages to the post parent using a 301 redirect 
(post parents are also searched for by post name). If an attachment parent post 
cannot be found, it redirects to your blog home page with a 302 redirect.

Attachment Page Redirect X

Redirect attachment pages to their parent page (301), when possible, otherwise to the blog home page (302).

WPKube

Go Redirects is a URL forwarder plugin for WordPress that enables URLs like <code>http://mysite.com/go/far-far-away/</code> to forward to URLs like <code>http://someothersite.com/</code>. It’s a great way to create clean-looking affiliate links or provide permement links for remote URLs that may change over time. It includes analytics for the number of times a URL has been forwarded.

Attachment Page Redirect X vs Go Redirects URL Forwarder