Dropbox is awesome, but no program is best for everyone. You may, after using Dropbox, decide that you like the idea but the functionality of this service and the implementation just isn't doing it for you. Perhaps you don't like being tied down to a central server, or find the monthly access fees for paid accounts a bit expensive. Don't fret - there are some alternatives worth checking out.

• SpiderOak - Slanted towards file backup as well as sharing, SpiderOak isn't nearly as easy to use as Dropbox despite the interface's best efforts. However, SpiderOak's storage plans are incredible - you only have to pay $10 monthly for a storage capacity of 100GB, which is half what you'll pay for a 100GB Dropbox plan.
• SugarSync - Very similar to Dropbox, SugarSync can keep file synced between multiple devices including both computers and mobile phones. SugarSync already offers official support for Blackberry, Windows Mobile and Symbian in addition to the iPhone, iPad and Android. SugarSync also offers better deals on data storage plans. Most reviews agree, however, that the service lacks the intuitive feel of Dropbox.
• Windows Live Sync - Microsoft's sync solution doesn't rely on a central server but instead lets computers sync directly with each other. It is quick, and there are absolutely no data limits because nothing is ever stored on a Microsoft server. However, the interface is more complex and computers can only sync files when they're online simultaneously.