Put icons on toolbar buttons
When you're defining the button or after setting a reference to it, you can use the .PasteFace method to put the contents of the clipboard on a button face.
Of course, before you do this, you have to get the icon or graphic you want on the clipboard in the first place. For simple graphics, you can draw them or import them programmatically into PowerPoint then copy them. For an example of how to do this in VBA, see Put an image on the clipboard
A simpler way to get an attractive icon on a button face is to use:
.FaceID = nnnn
where nnnn is the number of any of Office's icons. How do you know what number to use?
Easy. Visit John Walkenbach's site and look for his free Face ID identifier. This works in Excel, not PowerPoint, by the way.
Note that it may look a little strange and will return the wrong face id numbers if your system's set to Large Fonts.
Or get the Face ID Browser at PowerPoint MVP Shyam Pillai's site