Here is a list of all the eCogs that are designed so far, please leave a comment if you have ideas for more eCogs.

Blank eCog - For when you don't need all 4 eCog slots but want to enclose the GadgetBox

WIFI eCog - Using ESP8266 module to provide WIFI for your IoT devices

.096" OLED TFT Display - These inexpensive I2C displays don't use up any pins and look great!

uSD Card - Just in case you need some data logging.

Sensor eCog - This board is designed to use with these 37 in 1 sensor kits you can get. This board accepts almost all of the sensors from this kit.

PSP Slide Thumb Joystick - Connect a nice and compact Analog joystick.

PS2 Joystick - This joystick takes up a lot more space but it also has a select line when you press it down.

Button and LED eCog - When you need simple input and feedback.

IR Remote Control - Send and Receive IR commands. Uses the TVBGone design from Adafruit as the transmitter so it can blast out commands pretty far. Also has audio jacks so you can connect the IR transmit and Receive Blaster cables easily available on eBay.