Overall for the intermediate to advanced user I would recommend Adobe Photoshop CS4 as there image manipulation program of choice. With features such as the brushes, layers and selections Photoshop has all of the tools you will need to create nice looking graphics. You can open up documents using Photoshop’s tabs interface which quickly lets you switch between documents easily and effectively. This program is expensive, but you get what you pay for which is an powerful photo editing and creating program.