SparkFun Electronics sells electronic components aimed at people creating DIY projects. The unique thing about SFE is that they don’t just sell a component (such as an accelerometer), they read the data sheets for the component and figure out what other parts would be helpful to add on a board, making it vastly easier for mere mortals to incorporate into a project.
The electronics industry supplies components to manufacturers who build things in huge quantities. Increasingly, however, there are people interested in building things in very small quantities, where a low unit price is not as important as an understanding of how the component works. SFE caters very effectively to this latter audience, not just with their designs, but with tutorials, projects, and their customer forum. I’ve used SFE as a source for the Arduino, a very inexpensive microcontroller board available in a variety of sizes programmable with open-source tools. They also sell a variety of add-on components for this system. SFE is an example of an enthusiast source that not only serves a community, but enabled it to exist in the first place. They’ve done this in at least three ways: 1) connected with tool makers to provide a retail outlet for their work, 2) designed example projects and boards to make the use of raw electronic components more accessible to a larger audience, 3) provided a way for people building stuff to share their experiences.