A good place to find some examples of PowerPoint presentations is cubicleninjas.com. It has a list of what it considers the top 20 PowerPoint presentations, such as The Power of Networking and Infographics made easy.
Garr Reynolds talks about several great tips for making good PowerPoint presentations on his website, GarrReynolds.com. One tip is to keep it simple. When presenting a PowerPoint project, the speaker is the main attraction, not the PowerPoint, and the presenter should not read everything straight from the PowerPoint.
Another of Garrs tips is to limit transitions, such as animations and sound, within the PowerPoint. This returns to the first tip, as the simple transitions are the best ones. If the movement to the next slide is taking too long, the presenter is going to lose audience attention.
Graphics should be of high quality. Pictures are nice, but when one is cut off in a strange place and stretched so far that it doesnt look anything like it originally did, it doesnt make a nice presentation. If using graphs, it is important that the graphs are appropriate and relate well to the information being presented. For example, pie charts should be used to display percentages, but perhaps not for more detail-oriented statistics.