Digital isolators based on transformers and capacitors use magnetic and electric fields to couple data across isolation barriers where optocouplers use light. Digital isolators can be manufactured using CMOS technology allowing the integration of signal conditioning circuitry in the chip to greatly reduce power consumption and improve data transfer rates.

The iCoupler family from Analog Devices is a family of digital isolators that feature up to 16 kVpk surge protection and that can withstand voltages up to 5 kV. Signal speeds go up to 150 Mbit/s.
 
Universal I2C bus isolator and level adapter

We tried one of those digital isolators in our Universal I²C Bus Isolator project that we will publish soon. Not only does this board provide galvanic isolation, it is also a level adapter. And it is not limited to I²C applications as it can handle all digital signals up to 1 Mbit/s. Of course it works great.