The most popular 3D modeling programs for use with 3D printers are , and . There are many others as well according to Shapeways.com. For a list of supported applications click here http://www.shapeways.com/tutorials/supported-applications,
Lately, 3D printers are getting inexpensive enough for individuals and or schools to afford. The Makerbot Replicator II (a desktop 3-D printer) now sells for $2,199.00 which is low compared to a few years ago, when the price was around $5,000.
There is a basic machine called the Portabee (pictured) that sells for $480.00. It has a bunch of limitations, i.e. it can only print in one color and there is a size limit. But it is very portable and would be a fun tool for a novice or for use in a school setting to build 3D creations in a cost-effective way.
There is also a cost for the material for these printers. Plastic materials are used for these lower cost printers. However, everything from chocolate to bone like material, to full color sandstone, to glass to regenerating actual skin are being used in printers. http://3dprinting.com/materials/10-game-changing-3d-printing-materials/(10 game changing 3D printing materials Fri 13 July 2012 in Materials | Chris Waldo)
Here is a demo video of a printer from Makerbot called the Thingomatic.