The I2C bus

Most popular of the serial buses. Uses one wire for clock and one wire for bidirectional data. Based on Phillips' iic network. Lots of chips use the i2c protocol.

Good short introduction here. Not Arduino based.

Using i2c to connect arduino to eeprom chip that holds 256k bits, here.

Interesting use of i2c OLED display.

SPI or i2c. Which one is ""better"?

This video is about the IIC bus and gives a brief overview.

and this one is more of an ad but has some essential information.

This You Tube video is a bit more comprehensive than the above two.

A good example is here.