Actually, _JT_'s code won't work because it's in the wrong order.
$().SPServices.SPCascadeDropdowns({
relationshipList: "Types",
relationshipListParentColumn: "Departments",
relationshipListChildColumn: "Title",
parentColumn: "Department",
childColumn: "Types",
simpleChild: true
});
You can switch to a simple child dropdown by adding the simpleChild option to the SPCascadeDropdowns call per the docs.
M.