Dropbox is an easy to use freemium cloud storage solution. It has a client sync utility for multiple platforms.

Copy.com is a discontinued cloud storage service that offered near-unlimited space and huge bonuses for referrals.

OwnDrive is easy to use free online storage service for businesses, professionals, and individuals to store, backup, collaborate and share files with others.

Google drive is Google's cloud storage solution for storing files in the cloud.

Koofr offers safe EU based cloud storage with 2 GB free cloud storage space for life and options to connect multiple cloud accounts.

Pogoplug is cloud storage for your mobile life. Access all your files, photos, music and movies wherever you are.