The new OrganizeMe is the task manager for you if you're really serious about getting your stuff done! It is easy to use, but still supports your organizational method of choice -- from Getting Things Done (GTD) to PRINCE. It's available on Windows, Mac, iPad, and iPhone with free Cloud Sync to share your tasks between all installations. This makes it easy to use the same tool wherever you are -- no matter if you have a PC, Mac, or just an iPad in front of you.
Basic task-management features:
OrganizeMe for Mac, iPad, and iPhone is available in English and German.