Harpinder, if you are referring to publishing web map services in general, then I would recommend Minnesota Map Server (http://mapserver.org/) or GeoServer (http://geoserver.org/display/GEOS/Welcome). The latter (GeoServer) requires much less programming experience than MMS. My work colleagues also indicate that GeoServer is much more compatible w/ ArcGIS / ESRI symbologies than MMS.

Thanks emil for the solution for raster sharing !. But will versioning of vector feature classes i.e. multiple users editing a single layer be also possible will we able to give privileges like read only, write etc to various classes of users like in Arc GIS server ?

If your question involves the management of raster data and big data I think Rasadam will be a good option. It follows OGC standards and according the developers is very fast, time series analysis is available, supports wcs, wpcs and multiple formats

In regards of your last question about vector data if you want to multiple database access you need PostGis.