Spring and Terracotta play together very well, if you're worried about HA/Clustering have a go
Spring and REST: the version 3 of Spring will let you write RESTful service with just a couple of annotations
Spring Testability is unbeaten: there's nothing as easy to test as a POJO, in addition to that Spring offers autowiring and transaction managment inside the tests
Spring OSGi: assuming that OSGi is a good idea Spring is already there
Spring is not a silver bullet but you'll have to point me a gun in order to consider EJB3 as an alternative
