For Linux users, there are plenty of Dropbox alternatives, MEGAsync being the latest entrant. The service was the brain child of Kim Dotcom, founder of now defunct Megaupload, and it was launched on 19 January 2013 to coincide with the one-year anniversary of the seizure of his previous enterprise. MEGAsync now has a dedicated Linux client as well (unlike Google Drive).
MEGAsync's client for Linux released
The biggest and obvious attractions of MEGAsync are the massive 50 GB of free storage and its client side end-to-end encryption capabilities which makes it one of the most private and secure cloud storage services out there. Obviously one should not trust any cloud storage services with their sensitive data, but client side encryption capabilities gives MEGAsync a clear advantage.
MEGAsync also offers good Nautilus integration functionality which makes it super easy to sync any particular directory in your drive with Mega's online cloud service.
If you are on Ubuntu 14.04 LTS, simply download the appropriate DEB package and double click to install it OR use command-line like this:
sudo dpkg -i ~/Downloads/megasync-xUbuntu_14.04_amd64.deb
MEGA currently provides a multi-platform software development kit, and have plans to release the source code to MEGAsync under an open-source license. Read more here.