Hey you sap! What about SAP!
SAP went open source lately. Free for all. I still like PostgreSQL better (maybe because I know nothing of SAP). But, I don't know many people that would tell you that SAP isn't one of the most capable DB's in the world.
I think recommending MSSQL to a client is a disservice. The licensing scheme is a trap waiting to be sprung. Postgres can easily do well what MSSQL tries to do well.