A small DC - DC boost module that converts a 0.9..5V power source to standard 5V, making it capable of supplying power to an Arduino microcontroller and other small electronic devices that use a 5v input. It integrates a PFM DC-DC boost control chip. FIT0471
Pololu 3.3V Step-Up Voltage Regulator NCP1402
This powerful boost regulator efficiently boosts input voltages as low as 2.9 V to a higher, adjustable output voltage between 9 V and 30 V while allowing an input current as high as 5 A.