it's likely that this dialog is empty because you're configured to read namespaces from the project's class path, and you probably don't have any Spring jars on your classpath yet.
If you go to Preferences -> Spring -> Beans Support -> Namespaces you can toggle the global setting "Load NamespaceHandler and XSD's from project's classpath". If you turn this off you will get a set of basic defaults, but if you keep it on then STS will search your project classpath for namespace definitions bundled among the Spring Framework jars.
You can also toggle this setting on a per-project basis by selecting Project -> Properties -> Spring -> Beans Support -> Namespaces.
Leo Dos Santos
Committer, SpringSource Tool Suite