This is a good stage to go through your content and choose applicable images. You can also have a graphic designer create and add custom photos or custom graphics if you need to illustrate something like a process or stats.

Stock photo sites have fantastic images to support the content you are discussing though and can usually be found for free or purchased fairly inexpensively.

Some of the best ones to check out are:

• Deposit Photos
  
• Veer
  
• iStockPhoto
  
• MorgueFile
  
• Flickr (advanced search with the Creative Commons boxes checked)