Admin-Link-Box plugin by lynk, puts a hidden wp-admin/login link in the top-left corner, visible on mouseover. This simple plugin (copycode is useful if you want to have an easy to find admin link that is not visible on the page. Very easy to modify (position, colors etc.).
Requires WordPress Version: 1.5 or higher Compatible up to: 3.0.1 Last Updated: 2010-10-22