LiquidPlanner is a strong online project management service, much better than BaseCamp for one. It gives you desktop project management functionality on the web and does it well.In the latest release they added three important usability features:

Multi-select - allows you to select, drag-and-drop and delete multiple items at a time. If you have used Microsoft Project you would immediately know how much it speeds up managing your project plan.

Add new tasks by email - Now you can easily add new tasks by email. Just enter the task name, owner, and estimate in the subject line of your email and send it to a custom LiquidPlanner email address. Attachments and images will be captured in the collaborate tab.

Right-click access to common operations - Now you can use right-click to use common operations like adding or deleting items, filtering views, printing schedule etc.

We have extensively reviewed LiquidPlanner in the past. I think it is one of the most complete online project management service out there.