The really big one is "deterministic" static analysis of code. What I mean by deterministic is that in non-dynamic languages it's possible to find all references to variables, functions and classes with 100% certainty just by looking at the code.
This leads to 2 killer features:
- 100% reliable refactoring
- Sophisticated code navigation (call graph, inheritance graphs, go to definition are 3 that I used dozens of times a day, for example)
Of course, even languages that are traditionally thought of as static, like Java, have some dynamic features, so the above "100%" isn't quite reached in practice.