Service Oriented Architecture is a generic term for an architecture offering Services and all the supporting infrastructure such as directories and permissioning, etc.
It could be argued that the first SOA was the Distributed Computing Environment (DCE) many moons ago. Web Services is the current fashionable SOA, coming as it does from a long line of DCE, COM, CORBA….
So saying, Web Services looks like a winner since all the major players are supporting it (for the first time). But, be careful, if you want standards, WS has plenty, but hardly any are defined. A WS expert told me recently that there were at least 50 different standards being worked on today… and you wouldn’t believe the sort of esoteric stuff they’re working on!