There are myriad hardware options first of all: ALiX, Corvalent, VIA, SuperMicro; all of them make small embedded or miniPCs you can use for routing platforms, but even those are more complicated than it has to be.
My home router for a long time was a single-port Atom board, with trunked vlans. My switch had seperate vlans/ports for my cable modem & ADSL uplinks, plus my wireless vlan and my normal lan.
If you don't want to run purely stock linux/BSD, there are also a lot of pre-packaged "router OS" options. Vyatta, pfSense, DD-WRT, BSD-RP are but a few of the options. Wikipedia has a
List of router or firewall distributions.