Raspberry Pi 5V Logic Level Adapter – ICS Controllers
Amazon.com: EPLZON TXS0108E High Speed Full Duplex Logic Level Converter 8 Channel SPI 8 Way 3.3V 5V IIC 8-Bit Bi-Directional Converter Module Compatible with Raspberry Pi and Arduino (Pack of 5 Set) :
Amazon.com: RPi 3.3V to 5V 26 I/O Bidirectional Voltage-Level Shifter Module for Raspberry Pi, Logic Level Converter : Electronics
8 Channel Logic Level Converter Bi-Directional Module 5V to 3.3V For Raspberry Pi /
Logic Level Converter Only Half the Voltage on HV Side - General Electronics - Arduino Forum
Logic Level Shifter Converter 8 Channel for Arduino Raspberry Pi Module 5v 3.3v | eBay
Pololu - 3.8. Raspberry Pi interface and level shifters
SparkFun's Logic Level Converter | Hackaday
A Bidirectional Level-Shifting Buffer for Raspberry Pi – Kerry D. Wong