Icons for your websites, web app and icons for your CMS. Some of the following are free icon sets, while others are paid sets or links to people who make icons.
Sets of free icons that can be used in your web application or website. They also have a set of attractive flag icons. Licensed either as free to use or as Creative Commons Attribution 2.5 License.
Some samples of professional work and some beautiful free icon sets designed by Bartelme Design. Featuring some xml document and device icons and then some brilliant apple icons that make me wish I owned a mac.
Dan Cederholm moves his icons into their own shop, where you can pick up professional grade icon set from as little as 18USD.
Some of the sets are customizable and there are various sizes available, perfect for use on the web in your CMS, website or web-app.
A free, Creative Commons licensed icon set that comes with more than 150 icons and associated Photoshop files for tweaking. The icons come in various sizes.
A set of 14x14px icons with transparent backgrounds, this set includes a range of icons from file types to CMS icons and others useful for different types of websites. Free for limited use.
A set of 113 grey scale 10x10 icons that cover most of your basic icon requirements (delete, add, cut, paste etc.) and some extras that you could be useful in your grey scale CMS :-)
Creating favicons always seem to be a pain in the you know what, but after uploading a random image to this tool and having it generate a usable favicon, I think I've found my favicon creating answer.