Embrace your legacy systems. In fact, they may be the majority of services that you leverage within your SOA. This means service-enablement of systems that you would consider old and outdated, but indeed serve a purpose within the business and thus serve a purpose within your SOA. Those who attempt to displace and replace existing systems, just to support new technology, are destined to make their work much more complex and far reaching than it need be.
The Insider's Guide to Next-Generation BPM
Careful with this one. There's a lot of over-patched, fragile crap out there in production that needs, at a minimum, to be refactored, or completely redesigned. Service-enabling this stuff may cost more over time than just starting from a clean slate.