In my Top Daily-Use Products post, I listed Dropbox and it would still make the list if I revised that list, and that's not even including the premium version; the free version is that good. Tech deal-of-the-day site, AppSumo is running a giveaway where 10 lucky winners will get a lifetime 50GB account, which normally run $9.99/mo.
It takes 10 seconds to enter – just hit this link. Good luck!
BTW, I totally recommend you sign up for a free account regardless of whether you enter the contest.
PS> Another cool syncing service to check out is SugarSync.