Where to get plugins
The community behind WordPress plugins is a huge one. There's no one central plugin-building company, developers all over the world create plugins and then distribute them across the Internet. And very often, they receive no direct compensation whatsoever.
The best place to go for WordPress plugins is the official directory at http://wordpress.org/extend/plugins/.
There are over 27,000 different plugins available in the directory at the time of writing and this number is constantly expanding with around 110 new plugins being added every week. This really is an impressive number considering the fact that many of those plugins are very advanced pieces of web software and not just simple, one-script add-ons.
There's a search field available in the center of the page in the directory (visible in the preceding screenshot), which allows you to search plugins by topic and by tag. You can also view a list of the most popular and featured plugins. In short, the official plugin directory...