Google Docs is a free, web-based word processor, spreadsheet, and presentation application that allows you to share and collaborate with others in real-time. The Docs team just announced on their blog that you can now search for and insert YouTube videos into your presentation slides. This means that you'll be able to insert your favorite videos in your presentations and play them to your audience when you're giving your presentations.
To see this new feature in action, check out this published presentation.
Haven't heard of Docs? Watch this video that explains what Google Docs is in plain English:
The YouTube Team