My employer has business-level cable modem service, and we have a block of five static IP addresses. Until this morning, we've been using IPCop running on an old box in order to facilitate NAT'ing and port forwarding from the five external IP's to various servers within the internal network. Unfortunately the IPCop box died a sudden death this morning, and we're left limping along on a temporary Linksys wireless router. We've been able to restore email by using that single static IP as the external address it's using, but we need to service all five in order to run the business.
I'm looking to purchase as inexpensive of a router as possible that can handle port forwarding across multiple external IP addresses. While particular product recommendations are welcome from my point of view, I'm more interested in what I need to be looking for to be able to determine if a particular model can support this configuration.
TL;DR Version: What is the term (assuming that there is one) that is used to describe the a router/firewall that supports forwarding ports from multiple external addresses to various internal addresses?