I create a lot of graphic elements for presentations and since the inception of PPT XP I have been able to do many directly in PowerPoint with some creative use of AutoShapes and transparency settings. PPT MVP Shawn Toh has posted a sample presentation with some really great 3D spheres at Indezine.

Here is one of the spheres created entirely with autoshapes:
One of the 3D Spheres in the Presentation
Here are the autshapes used to create the above 3D spere:
Autoshapes used to create the 3D Sphere

Here is the description and download link on Indezine, click here.

Troy @ TLC