There are several products and add-on hardware developed specifically for Raspberry Pi. Most of them are designed specifically for Raspberry Pi. Some of them are available through DIY product sellers such as Sparkfun and Adafruit Industries. Most products are developed through crowdfunding sites such as Kickstarter and Indiegogo. We made our best effort to introduce a new piece of hardware in each project. A simple web search should pop up a new product for a specific application.
The Raspberry Pi model A+ and B+ has more GPIO pins than the model A and B. The model B+ has two more USB ports while model A+ consumes less power than the model A. Hence, it is possible use a power over Ethernet module (PoE). Check out http://www.silvertel.com/component/content/article/22-latest-news/304-raspberry-pi-poe.html for more information.
If you own a Raspberry Pi B+ but the hardware...