E.g. - is short for exempli gratia which means for the sake of example in Latin. E.g. can only be used for examples.

 - Marketing now makes great use of social media. E.g.: facebook, twitter, google+, etc.

  

 I.e. - is short for id est which is Latin for that is. It is used to explain something or further expound the previous statement or clause.

 - Marketing now makes great use of social media, i.e., media platforms that are easily accessible for social interaction.