If you are editing this page, remember that this is a directory of companies that primarily sell new parts, while the surplus page is intended for shops that sell used or salvaged parts and equipment. There is necessarily some overlap between the two. If you think a retailer sells both types of items, then it's ok to add it to both lists.
These are smaller companies that generally cater to the hobbyist market, although some of them are getting quite large (eg. Sparkfun).