I'm building a collection of clip art resources in this section.
I found some old clip art that I made with Inkscape after a bad experience where Windows would give me the Blue Screen of Death every time I shut my laptop down.
The Windows Blue Screen of Death clip art is below. I am releasing these masterworks into the public domain, so feel free to post them on your Web sites. A link back to this page would be appreciated, but is not necessary.
Another nice set of mini icons can be found on sweetie.sublink.ca. It looks like there are over 170 mini-icons included, and they are licensed under the Creative Commons Attribution-ShareAlike 2.0 license.
Here are a few:

Xara Xtreme is a vector graphics program that until recently was only available for Windows. There is now a version of Xara Xtreme for Linux that has been released under the GNU GPL. It's still only in version 0.7, but I've just downloaded it and installed in on Ubuntu Dapper and it works great.
Here is a screenshot of Xara Xtreme LX on Ubuntu 6.06:

The Buttonator is a free online tool that lets you quickly generate buttons for your web site. It's a clever AJAX-based site that is interesting to use even if you don't need a button.
Here is a sample button from the Buttonator:
Related post: Button Maker Tool.
Inkscape is a great free vector graphics program for Windows, Linux and Mac OS X.
Vector graphics are images that are defined by mathmatical equations instead of by pixels. That means that you can change the size of the graphics without losing any image quality.
SVG or scalable vector graphics is an XML markup language for making vector graphics. Inkscape creates all of the XML for you, so you can just draw on a screen (something like using the Adobe Illustrator program).
For some reason, this site has been getting ongoing traffic from people searching for "free scooby doo clip art" (and sometimes Scoobie Doo).
I like to keep my readers happy, so here is where you can find your free Scooby Doo clip art:
I found a nice tool for creating custom buttons.
Just enter in the desired text and attributes for button, and the web page will generate the button for you.
Example button:

Related post: The Buttonator.
I just found another "tips" web site called quickonlinetips.com that mentions a source of great free icons:
FamFam.com is offering free icons for download. The collection includes flag icons, a set of 700 "silk icons", and a set of over 140 "mini icons".
Here are just a few of the many flags that are offered for free download:

Be sure to read the Creative Commons Attribution 2.5 License that they are licensed under.
There are many places to get free graphics for your web site online. If you don't already know about it, check out OpenClipArt.org. Here are a couple of samples from the Open Clip Art Library:

If you use the Open Clip Art Library, you should also download Inkscape, a free vector graphics editor that can edit SVG files. The GIMP, or GNU Image Manipulation Program, is another free program that is useful for editing the graphics after you have converted them into PNG, JPG, or GIF format.