OS X Dashboad Widget
Doug Neiner created this Dashboard widget for Mac OS X that uses the API to pull quotes from this site. Just download, unzip, and double click the .wdgt file to install. As a bonus, he released the code as open source under the MIT license, and it is available over at Github.
Windows 7 Gadget
Google Chrome Extension
There is a Google Chrome Extension for QoD.
If your thing is building Google or Yahoo widgets, then maybe you should consider building a widget for Quotes on Design using our API Documentation. If you build something you would like to share, please send a tweet to @chriscoyier so we can list it on this page!