Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.
One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.
As far as third party software. Here are two I've know.
http://www.quotamanager.com/products/qfs/
http://www.tools4ever.com/products/spaceguard/
I would also try typing the following into Google:
award Best Quota Management Software