The Professional edition has all the features the Standard edition has and many extra.

It allows you to easily email tasks to others or to yourself. Set Start Date and Completion Date for your tasks. Assign tasks using Assigned To field. Track your progress more precisely using Percent Done field and Status field. Use Time Estimate and Time Spent fields for instant clarity about time needed and time spent for each task. Context field helps you to better categorize your tasks.

The best part is: You decide which fields you want to use, and which to completely hide (this is a unique feature).