I tried the Microsoft FTP server as I had IIS installed, but that didn't give me enough control.
There's also FileZilla server, which is free, and appears to have as much configurability as Serv-U, and to be honest, it doesn't seem as robust - I really liked Serv-U but wanted to try something that was free.
However, I'm not 100% sure about how good it is - had a few transmission errors which I shouldn't be having really.