Sharing individual documents outside the organization is now possible in the newest versions of SharePoint. Office 365 subscribers already have this capability.
When selecting a document from a library, you’ll notice the Share menu selection. Use this to share access to a document outside your organization, without giving up the whole folder or library! If you email a link to someone who doesn’t have access to the library (or folder, if you’re securing at the folder level), he won’t be able to use it. Site Owner or Full Control permissions are needed to share a document with external users.