Here is a list for Visio shapes expansion.

Network Equipment Shapes for Microsoft Visio – download

• More than 2000 shapes of  3Com, APC, Cisco, Dell, Hewlett-Packard, IBM, Nortel, Panduit, and Sun Microsystems network equipment.

Geographic Map Shapes for Microsoft Visio – download

Visio Educational Shapes – download

• Chemistry: Molecules, Organic Compounds.
• Mathematics: 3-D Geometry, Analytical Geometry, Angles, Circles & Ellipses, Common Functions, Exponential, Logarithmic, and Power Functions, Hyperbolas and Parabolas, Plane Geometry, Sets, Sine, Cosine, and Tan.
• Physics: Circuit Diagrams, Lenses, Mirrors, and Prisms, Light Sources and Waves, Magnetism, Pulleys and Levers, Vehicles.

How to install Visio Shapes

1. Download the .zip file.
2. Extract the  files
3. Copy the extracted files to the "My Shapes" folder in your "Documents" or "My Documents" folder, which will be located under the following path:
   C:Documents and SettingsusernameMy DocumentsMy Shapes – Windows2000/XP/2003
   C:UsersusernameDocumentsMy Shapes – Windows Vista/7/2008