The default admin theme Seven is really great… clean, direct and simple. However, I do find it a bit bland. I mean, yeah… its supposed to be sort of “boring” because its just a clean admin theme. But the light grey header really washes out the page. I’ve made a few tweaks to the theme over time in order to make it a bit “better” (imho).
For those who actually like or use the “Overlay” module (I do from time to time), there are some enhancements there with nicer rounded edges and a bit of a shadow.
Developers - are you branding your work?
I have my RT logo in there which shows up on the maintenance page and in the lower right corner of admin pages, but its totally possible to replace it with your company logo. You may even want to output contact info, a link to a support form, news feed or other content into the theme (probably at the bottom of the page template). Then you can install this as the base admin theme on all of your clients, and be able to subtly keep yourself in mind to the admins.
While this is very simple, I do think it improves the overall usability and “feel” of the admin site. And, by adding your own logo, its a very professional and clean way to build your own branding!
The theme is attached here - feel free to grab it, rename it (or not) and hack it to bits…. have fun!