The ADXL335 is the latest and greatest from Analog Devices, known for their exceptional quality MEMS devices.
Price:
$14.95
This is a basic breakout board for the FTDI FT232RL USB to serial IC.
The SparkFun bi-directional logic level converter is a small device that safely steps down 5V signals to 3.3V AND steps up 3.3V to 5V at the same time.
$2.95
The TSL2561 luminosity sensor is an advanced digital light sensor, ideal for use in a wide range of light situations. The best part of this sensor is that it contains both infrared and full spectrum diodes! That means you can separately measure infrared, full-spectrum or human-visible light.
$5.95
If you have an ItsyBitsy or Pro Trinket you probably know it's the perfect little size for a portable project. This LiPoly backpack makes it really easy to do! Instead of wiring 2 or 3 boards together to make a charging system, this little PCB sits on top of the PCB and allows a LiPoly/LiIon battery to plug in. When the Pro Trinket or ItsyBitsy USB port is powered, the battery is recharged automatically. Unplug the USB port and the microcontroller will switch over to the rechargeable battery.
$5.54
This is the RFduino USB shield, a small add-on board that plugs into any USB port and is used to load your sketches onto an RFduino module.
$25.95
The SparkFun ESP8266 Thing is a breakout and development board for the ESP8266 WiFi SoC
$15.95
The Attiny85 is a fun processor because despite being so small, it has 8K of flash, and 5 I/O pins, including analog inputs and PWM 'analog' outputs. We designed a USB bootloader so you can plug it into any computer and reprogram it over a USB port just like an Arduino. In fact we even made some simple modifications to the Arduino IDE so that it works like a mini-Arduino board. You can't stack a big shield on it but for many small & simple projects the Trinket will be your go-to platform.
$7.78