Jameco is a good source.
Other inexpensive sources are:
Circuit Specialists: http://www.web-tronics.com/index.html
Mouser Electronics: http://www.mouser.com
Newark Electronics: http://www.newark.com
Electronic Surplus, Inc.: http://www.electronicsurplus.com
All Electronics: http://www.allelectronics.com
You can also request free samples from the manufacturer's websites, although, sometimes this requires you to be a business or have a business name.
MP