I have the netgear gigabit GS105 - 5 port switch for this exact purpose. networks together 2 pcs, a mac mini and my synology NAS, with the 5th port is plugged directly into my router, so everything has a network connection through the LAN. it's like $30. Completely, stupidly simple, plug and play, worked first time I plugged it in, haven't thought about it since. If I need more ports I simply remove what's not being used and it auto-configures. Works great.
http://www.netgear.com/service-provider/products/switches/unmanaged-desktop-switches/GS105.aspx#