I love Dropbox. I use this cloud service to connect my iPad2, iPhone, laptop, desktop, netbook, another desktop, Windows Home server, and my family's laptops to a single Dropbox. We can exchange files around by merely dragging and dropping. It is a great example of an easy to use application that leverages the cloud. It is free for up to 2GB of storage and then has subscription plans for higher storage amounts.
However, besides sharing files inside the "closed" Dropbox of my family and my computers Dropbox has a public folder option. Anything you drag into the public folder can be independently shared with anyone via a web link. The person accessing the public link has no access to the other contents of your Dropbox. Here is how to create a public Dropbox item.
In your Dropbox you should have a folder called Public. Copy the item you wish to share with those outside your Dropbox into this folder.
Right click on the file you wish to share and select Dropbox and then Copy Public Link. Share this link with anyone you want to have access to this file.
By pasting the Dropbox Public Link into a web browser anyone can have access to the one file. The person you share this link with has no access to anything other than the one file you shared. They require no passwords or logins beyond the link you share with them to access the file.