I am looking for a product that would provide our campus a list of
gateway security services on our internet connection.

We have a campus with well over 2000PC's and 5000 users, all fed by a
single ATM connection through a Cisco 3825. I am looking for a
hardware appliance that would provide us IPS, firewall, NAT,
URL-filtering, anti-virus, and anti-spam services, together with the
ability to be expanded if the PC's and users increase to 4000 and 8000

So far I have studied Fortigate products, but I feel the need to see
some alternatives/rivals to them.

Thanks in advance.
Advise on unified Thread Managment - security hardware appliance