JY-MCU 5V 3V IIC UART SPI Level 4-Way Converter Module Adapter

Pros: It works exactly as you would expect: connect 5V and GND to one side, 3.3V and GND to the other, and you can shift up to 4 bidirectional signals between 3.3V and 5. This adapter is a must-have if you're working with 3.3V boards like the Raspberry Pi. I've had one converting I2C signals for a couple of weeks now with absolutely no glitches.

Cons: None, really. For 4 bidirectional lines, the price is right.

Other: This type of adapter isn't commonplace yet, so I was surprised to see it on DX. If you only have a couple of data lines to convert, DX also sells a 2-line adapter for a little less, 178301.

Pros: Really nice form factor, plug it in your breadboard and do whatever you want. Does what it is designed to do. Converts signals from 3.3V to 5V. Tested with Arduino and pinguino with I2C humidity sensors, gps, motorola C115 LCDs and a lot of devices that runs on 3.3V.

Cons: Nothing really. Quality is not the best, but it's ok for the price

Other: Will buy more for other projects.