My router is a Buffalo WHR-HP-G54 with third party firmware called DD-WRT. The reason I mention it is because that is my firewall. I am using my router for NAT and I have the SPI firewall between my home network and the Internet. I don't like using the firewall on my computers because I do too much on my network to have to mess with the firewalls.
The center of my home network is my Windows Server 2008 R2 machine that serves as the domain controller. Right now it only serves two client machines (both running Windows 7 Ultimate), but I hope to add a laptop as a client soon too. My domain controller runs Active Directory with roaming profiles, DHCP, DNS, WSUS, file server, print server, FTP server, Web server, central backup using Crash Plan, etc. I built my server because it was much cheaper than buying from Dell or HP. It has an Intel Quad-Core Xeon processor with Hyper-Threading, 8GB ECC DDR3 RAM, and two 500 GB hard drives in a RAID 1 for my OS and other partitions that are not backed up and four 500 GB hard drives in a RAID 10 for my backed up data. I have space for 3 more hard drives in my server case, but if I want to add more drives I will need to get a controller card because I don't have the ports on my motherboard.
For Antivirus, I run NOD32 v2.7. When I first got NOD32, if you purchased more than one license for your home, you would be given access to an Admin version of the software that you would install on a computer in your home and would provide a mirror to host the config and virus update files for the rest of the computers on your network. I love this feature because after you set up the config file and download the virus updates to the server, you just link the other computers on the network to the server and they are automatically configured and updated. When version 3.0 came out, Eset got rid of this feature and I wish they would provide it again. It is available in the Business editions, but at a cost of more than double of what the home licenses cost. For now, Eset still supports version 2.7, so I continue to use it.