FTPBasket is a free FTP software that lets you upload files to a FTP server by just drag and drop. It installs as a basket icon, and you can just drag file to this basket to upload to a FTP server.
FTPBasket lets you configure connections of multiple servers, and quickly select the connection that you want to use for FTP upload. You can even upload files to FTP server by dragging them directly from Windows explorer.
Download FTPBasket here.