When you hit "insert chart" in Excel or PowerPoint, a pretty ugly graph shows up. Here are the steps I take to clean things up:

1. Horizontal axis: 2pt line instead of 0.75pt
2. Horizontal axis: smaller font until labels show up horizontally
3. Horizontal axis: no tick marks
4. No chart title, instead I use the consistent PowerPoint headings
5. No grid lines
6. No vertical axis
7. No legend (I use PowerPoint boxes to make those)
8. Data labels on top of the columns
9. Data label values rounded up
10. "Gap width" between series 50% instead of 150%

I am not going into the details of PowerPoint menus here, but you can usually change most of these things by right-clicking an element in your chart. (Click on images for larger picture)