It's a huge part of Wordpress, yet not many have delved into creating custom backends for the Wordpress Admin. This is an area we would love to see more people working on, there's definitely room for improvements.
Here is a list of some of the Wordpress Admin Themes available to download Wordpress admin themes:
This is by far the most popular admin theme available, created by Ordered List with more than 40,000 downloads! This is the most unconventional of the bunch with the navigation as a sidebar instead of at the top.
By ceprix, another very popular admin theme and its not hard to see why! Inspired by spotlight for Mac OS X and Milk by Max Rudberg. Site seems to be under re-construction but you can still download a copy of Spotmilk.
Js Style SpotMilk Admin is base on SpotMilk Admin,with a few cosmetic changes. Green or Blue Versions available.
Developed by sevban.com is pretty much an all blue version of the standard admin, clean lines, easy to navigate tested with Wordpress up to v2.2.
Developed by aenon fire design, this is again very similar to the default admin theme, the main difference is it lets you customise the colour of the header and menu's. This is great if you run multiple Wordpress installations and have several admin tabs open at the same time for distinguishing between sites. It's compatible with the latest version of Wordpress and comes in an easy to install plugin.
Based on the Spotmilk and Default Wordpress admin theme, NiceAdmin was created by Douglas Karr. Compatible with Wordpress 1.5 through to 2.3. This is one of our favourites at welovewp.
Based on iTunes, Wordtunes was refreshingly different to the other admin styles created, unfortunately we have been unable to locate a download link for this theme, use the comments to let us know if you can find one.
UPDATE: Thanks to Steve for finding a download link, updated the image and title to link to the Download, still appears to be no home for it though.
Developed by Broken Kode, it's been a long time coming and were not sure if this will ever see the light, there's some nice features visible in the screenshots. Hopefully we will still see some of the things added into the core wordpress admin in future releases.
This theme is probably our favourite, unfortunately it's an unnoficial, unreleased copy of the popular Digg site styled into Wordpress admin.Resources:
MyDashboard: Netvibes/igoogle/pageflakesstyle dashboard.