The World Federalist Movement "is is an international citizen's movement working for justice, peace, and sustainable prosperity. We call for an end to the rule of force, through a world governed by law, based on strengthened and democratized world institutions. We are inspired by the democratic principles of federalism."
World Beyond Borders doesn't seem to work well in my browser (Safari) but looks like a collection of ideas and links.
WorldGov.info is a discussion forum.