With smaller screen sizes, icons are becoming an increasingly important element of user interface design. Not everyone of you is likely to be using PowerPoint to design a web app (hey I do), but icons can also be useful in regular presentation design.
I am not talking about floppy disks and other ancient icons we still use, but stylised symbols that can be an effective visual short cut to a category of (pick the appropriate) products, benefits, user problems, etc.
One option is to create your own icons in PowerPoint, set the zoom to 400% and create miniature shapes using shape booleans. Often you can use a quick Google Image search to find inspiration for your icon.
Stock photo sites sell endless amounts of icons, but there are compatibility issues when using them in PowerPoint or Keynote. Most icons are design as a vector graphic in Adobe Illustrator. It makes them infinitely scalable (like a PowerPoint shape), but PowerPoint does not read this file format. Copy-pasting Illustrator objects (if you have the software installed) is unpredictable and results in a shape that is hard to manipulate (changing colour for example).
Cropping icons out of a JPG or PNG file is not a solution either, if you forget to compress the small image file, you end up storing a huge image file with all your icons multiple times on a PowerPoint slide. Cropping also kills the vector-like scaling of icons, and background transparency.
A recent trend in web design might provide a solution: custom icon fonts. Modern successors of Zapf Dingbats (what?) provide clean icons that are scalable and can be manipulated (colours, shadows, and - do not use this - reflections).
The web is full of free icons fonts but not all of them work with PowerPoint and Microsoft Office (Font Awesome for example). There is a solution for this problem: custom font creation tools such as Fontastic. You can select icons from multiple sources and use them to create your own custom fonts. If you do not see the icons you need available, you can upload your own SVG files from stock image site purchases.
Obviously, using custom fonts in PowerPoint has its issues: users need to have your font installed in order to see the characters correctly rendered. PowerPoint has an option to embed fonts inside presentation files, but unfortunately this does not work on Mac OS X.
It is interesting to see that a software trick to scale Arial in a web browser is turning into a broader software solution for scalable graphics, including very large objects across different display engines.