Is there a way to display the latest mail in CiviMail?
Option 1) 

There is CiviCRM extension which seems to do exactly what you need: Public Mailings Archive filterable by date, template, etc. It says is compatible up to Civi 4.5 so you might need to contact the developer or test first if you are using 4.6

Option 2)

As you are on WordPress, check out Christian Wach's plugin, it creates a custom post for each public CiviMail mailing. You could link in your mailing to the custom archive page for that post, alternatively you could modify the archives-pages-template.php to output only the last post (ie last newsletter) if you don't want to expose previous newsletters.

Option 3)

Try out the Content Tokens extension and check if it fulfills your needs.

Option 4)

In conjunction with Christian Wach's plugin mentioned above, you could create your own token, as explain in this great post by Coleman.