looking for router firewalls

[Becki Kain <beckers @ josephus . furph . com>]

I am looking for ideas on good firewall software for routers, and the
routers have not been purchased yet, so the brand is flexible. I realise
router firewalls are not thought of as "as good as" something like a netra
or a bastion host with firewall software on it, but it's what the customer
wants (so as to appease both camps of unix and windows).  it would be for
about 150 pc hosts and 35 unix boxes. 

thanks

beckers