Things possible in IntelliJ that aren't possible in Eclipse?

Answer 1

IntelliJ has some pretty advanced code inspections (comparable but different to FindBugs).

Although I seriously miss a FindBugs plugin when using IntelliJ (The Eclipse/FindBugs integration is pretty cool).

Here is an official list of CodeInspections supported by IntelliJ

EDIT: Finally, there is a findbugs-plugin for IntelliJ. It is still a bit beta but the combination of Code Inspections and FindBugs is just awesome!