Here's what I built: (Copied and pasted from one of my gists)

Motherboard: http://www.gigabyte.com/products/product-page.aspx?pid=4918#...

RAM: http://www.amazon.com/Crucial-PC3-12800-204-Pin-Notebook-CT2...

Hard drive: http://www.amazon.com/gp/product/B008U3038I/ref=oh_aui_detai...

Case: http://www.amazon.com/gp/product/B00HWYRYMY/ref=oh_aui_detai...

OS: Debian Wheezy

Software: iptables, isc-dhcpd, bind9, openvpn

edit: formatting

I use these little guys. A bit overpriced and only 100mb but they work well, run pfsense, openWRT etc and generally do what I want for years in a closet with no further intervention.

http://www.pcengines.ch/

I've been running PFSense on an old Acer Aspire (now called veriton) and it's worked decently well for home use (100 Mbit downstream internet). It's only real downside was a single gigabit NIC, so I had to use VLANs and a router-on-a-stick configuration on a managed switch.

Since the hardware is aging (and I want more NICs for no good reason) I recently found the edgerouter from Ubiquiti. It's running a modified version of Vyetta/vyos and shares its powerful CLI. It's also dirt cheap at <$100 and has been said (I haven't tried to max it out yet) to handle 500Mbit throughput.

So far I haven't found anything that it can't do. It will also POE a few Ubiquiti access points, if you are into those. Makes a really nice home setup for the home network engineer for <$200.

A little pcengines apu4[0][1] or a lanner[2][3] - both work very well with pfsense.

  [0]: http://store.netgate.com/APU1C4.aspx
  [1]: kit http://store.netgate.com/APU4.aspx
  [2]: http://www.lannerinc.com/products/x86-network-appliances/desktop/fw-7541
  [3]: kit http://store.netgate.com/Netgate-FW-7541-BTO-P1893.aspx