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

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

4Sync is an online syncing tool. Sync & sharing access with cloud storage.

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

trolCommander is a fork of the free and opensource (GPL) file manager muCommander.