If your are new or experienced PCB manufacturer you might find that using a reference design saves you time and money over trying to start from scrath with a new design yourself. In principle, the library have open source designs that can be used as reference or a building blocks for a new more complex designs. These provide access to basic code or diagrams and general structures for easy assembly. Take a look at the examples provided below:

Footprint repositories and Libraries.

PCB library generator

These are the PCB footprints that I have created with various Perl scripts.

Open Circuits is a wiki for sharing open source electronics knowledge, schematics, board layouts, ports and parts libraries.

PCB Libraries for Cadence Allegro and OrCAD

PCB Footprint Libraries for Cadence Allegro tools

Altium Limited (ASX:ALU) is the leading developer of unified electronic product development solutions.

ALLEGRO PCB LIBRARIAN 610 AUTOMATED LIBRARY PART CREATION AND VALIDATION

Another option is to get in touch with forums that discuss PCB designs, maybe you're lucky and somebody has already created what you need. Here are some interesting forums:

PCB Matrix We are focused on EDA efficiency, productivity, and automation.

OrCAD libraries Discussions on PCB design and simulation are available through our message board topics listed below.

Libraries of schematic symbols and layout footprints Where to get symbols for your schematic -- where to get footprints for your layout

Almost all open source libraries will contain layouts in custom Electronics Design Automation Software (EDA) so you either need to download a free viewer - which normally are very limited in functionality - or you can get a license from one of the companies that distributes software for PCB design to have full access to all features.