Ag Custom Admin
Ag Custom Admin is probably the most complete solution available to customize your WordPress dashboard.
With this free plugin, you can change almost everything: admin menu and pages, login page, admin bar etc. Another very interesting option is that the plugin lets you apply admin panel themes. Though most of them aren’t free and not especially beautiful, in my opinion.
Free download: Ag Custom Admin
Admin menu editor
If you need to customize WordPress admin menu, then Admin menu editor is definitely a plugin to consider.
When using WordPress to create a website for a client, there are lots of things in the admin area that you don’t want the client to mess with. Based on user roles, Adminize makes it easy to remove items from view.
Free download: Adminize
White label CMS
White label CMS is a free plugin which gives you the ability to give the admin area a more personalized and less confusing look and feel. A great solution for those using WordPress to build sites for clients.
It also allows you to add custom logos to the header and footer as well as the all important login page, giving your client a better branded experience of their new website.
Free download: White label CMS
WP Total Hacks
A nifty plugin which gives you control over 20 different settings related to WordPress admin area. Among other things, it allows you to add a favicon, change admin header logo, deactivate selected meta boxes for posts & pages, limit the number of allowed revisions, block pingbacks, and a lot more.
Free download: WP Total Hacks
To complete this article, here is a list of hacks and code snippets that you can use to take control of your WordPress admin area. In this article, I’ll show you how you can keep logged in for a longer period, programmatically remove admin menu items, change WordPress dashboard colors, provide custom help messages to your users, and a lot more!