I’ve actually been bouncing from asana, do.com, and producteev. I’ve stuck with producteev. They all have workspaces, projects, tasks, and subtasks. I can email tasks, attach files (and with the producteev web app, I can preview my file even in full screen.)Also with Producteev, I get a daily report, my iphone has push notifications, and I get an email notification which I actually like. These are all free for individual accounts so it can’t hurt to try. Asana and do.com will have both android and ios versions by mid summer 2012.