Sometimes, a little variety can go a long way. Consider placing a picture for your PowerPoint presentation inside a shape (such as a triangle, star, circle, etc).  It will take away some risk of being seen as mundane.

The following tip works with PowerPoint versions 2000-2004, and while I have not personally tested Office 2007, I would assume it is still available in that version.

Step 1:
Click on Drawing Tools from the “Drawing Toolbar” (most likely at the bottom of your screen). Select Basic Shapes (or any of the categories) to select a shape in which you want to place the picture.

Step 2:
Right click on the shape, then select “Format AutoShape” from the drop-down menu. Click on the down arrow next to the Fill “Color” and select “Fill Effects”.

Step 3:
From the “Fill Effects” dialogue box, select Picture from the four tabs presented at the top, and then click on the “Select Picture” button.

Step 4:
Browse to find the picture you want to insert inside the shape, then click Insert. From the remaining dialogue box, select OK.

Step 5:
Select Preview if you want to see what the shape would look like, or click OK to accept your choice.