I’d recommend you to try Wrike! (http://www.wrike.com) It’s really powerful project management software with real-time newsfeed, Gantt chart, Workload view, email integration and many other great features – actually all you need for efficient project management. The app is online, so all team members get notified about all task updates in real time both in Wrike’s Activity Stream and via email. As for the sub-projects, in Wrike all tasks are organized into folders (it can be projects, departments, clients etc), so subfolders may be used as subprojects.

I'd recommend you to try KanbanTool http://kanbantool.com . This application will help you to gain at-a-glance visibility of your workflow and to efficiently manage tasks (using card colors, priorities, due-dates, file attachments, comments and to-do-lists). KanbanTool provides also useful features that empower team collaboration (advanced account access privileges and sharing options, adding tasks or comments via email as well as email notifications for task assignments and comments).

Try BrightWork! Sync's with Microsoft Project to provide a powerful tool! http://www.brightwork.com/case_studies/index.htm

Try Breeze (http://letsbreeze.com), Trello and Basecamp hybrid.

Try Asana