For automatic syncing of large libraries, you might want to give BitTorrent Sync a try (
http://labs.bittorrent.com/experiments/sync.html).
When Microsoft binned Live Mesh i was at a loss for automatic syncing of my various media between PCs - the various alternatives were poor. BT Sync is brilliant - and much faster than Live Mesh ever was.
I also use FreeFileSync (Portable), as mbovenka suggested. It is a great tool for syncing data - I use it for checking sync between folders before setting up auto-sync with BT Sync.
FFS also has a "RealTimeSync" option.