Multiple FTP sites-TCP/IP question

I want to setup multiple FTP sites on my IIS server similar to the multiple websites that I have. The FTP properties page does not have an option to add a host header name like the websites do. I know I need to five the site a unique port number sothat it doesn't conflict with the other FTP sites otherwise it won't start. How do I know which TCP ports are ok to use and is there a place I can find them all listed?