I'm not sure if this is the best SE site for this question but here goes.
I am looking to implement a simple and easy to use file transfer solution such that people can upload/download files with resume support to our office server (which does not have a static IP address).
So far, I have come across free FTP servers (such as FileZilla) and free DNS routing services (such as dyn) that allow this but I am sure there are simpler solutions out there.
Commercial solutions are welcome as long as non-technical people can administer them.
UPDATE: The data transfer per day is around 10GB and although Dropbox is fine for personal use, I'd rather use a more robust application that allows more control and acceleration. Any ideas would be appreciated.
It seems you have two different problems.
You should try google drvie or dropbox