Very thorny issue. Bosses are asking for presentations with lush images and clever videos and no one is willing to pay for anything. A few tips:

• Use creative commons to find content that is free for use, with certain conditions
• If it's an internal presentation, many photo libraries wil let you download images without watermarks
• There are a ton of other free resources as well if you just look for them
• And last, (while this seems obvious but in my experience no one does it) create a repository of images for re-use. Label and file them correctly. This will save you so much time and energy next time there is a mad deadline.