I would start with the OpenStreetMap Wiki at http://wiki.openstreetmap.org/wiki/RoutingOpenStreetMap Wiki. From there, I would say that pgRouting (http://pgrouting.org/pgRouting) is one of the more popular OS DB routing tools. If going with the pgRouting approach, OSM2PO at osm2po.deOSM2PO is a popular way of creating the sql import statements for large regions of OSM data, as I heard that the usual database import utility used with pgRouting, osm2pgrouting, has trouble with larger datasets.