I know someone who does printing and he likes coral draw and adobe photoshop as "fullon" mentioned! Freehand is fun too, but it takes practice! Just wait a day or so and something new will be out !
Professional artists who use computers to draw are normally referred to as commercial artists, graphic engineers etc. Specialized tools and software are available commercially to them. Programs such as Adobe Photoshop and Corel Draw have been around for quiet some time. Newer versions of these 'software' include Adobe Photoshop CS and Corel Draw 9 etc. Adobe has also come out with various related software such as Adobe Photo paint to help professionals. Windows also offers a basic "paint" program as part of accessories but this is not suitable for high end users as the features are very limited. Engineers and architects also require specialized software in the form of Auto Cad etc. Most of these applications can be manoeuvred through with a mouse, but certain others can also support hardware like sensor tipped pens etc.