Dropbox may be the next target of the government's invasive PRISM program, which means that it's more imperative than ever to learn how to safeguard whatever files you have stored there.
I prefer copy.com. Quite new, but perhaps the new dropbox.
If you register with the link below you get 20 GB instead of 15 GB (I get 5GB as well).
Furthermore you earn 5 GB (yes five GB !) of extra free storage for yourself each time you introduce someone new to Copy. in contrast to dropbox without any upper limit. However, this is a limited time opportunity during the promotion phase.