Animation software has gone through a major evolutionary cycle during the last ten years. Different packages have concentrated on different aspects of animation, or have looked at a particular set of applications that can benefit from their software, and so there is considerable market differentiation between different animation software.
Maya Software by Autodesk
Maya is one of several popular software tools being used today in the motion picture and video game industries. A high end and robust tool originally developed by Alias Systems, Maya won the company an Academy Award in 2003 and was cited as making a "significant and dominant impact on the motion picture industry." Maya provides powerful tools essential to the animator, including keyframe animation, nonlinear animation, and path animation tools. Maya also provides full render controls for shading and lighting, and realistic effects tools for smoke and hair. Perhaps one of the best features to Maya is its open architecture, which allows for third-party integration and an incredible level of customization.
Softimage/XSI by Softimage
A subsidiary of Avid Technology, one of the leaders of the high end video editing world, Softimage's flagship product XSI is a leading 3D graphics software used for films, video games, and advertising. XSI can be used for the creation of 3D environments, animate characters, or for 3D modeling. It offers the feature of being readily customizable through open scripting access and third-party add-ons. It can also be used for animation using the Animation Mixer feature, and its rendering system is based on the widely used Mental Ray application developed by Berlin-based Mental Images. The XSI product was released in 2000 to replace Softimage 3D and compete more effectively with products like Maya.
3ds Max by Autodesk
A popular and powerful modeling application from Autodesk, 3ds Max is primarily used in video game development and in TV production studios for the creation of rich, complex characters and 3D objects, as well as for design visualization. 3ds Max boasts a more user friendly interface than other packages, with a UI that makes it easier for the artist to focus on the project at hand and the creative process.
Perhaps the package that most people will have come across is Adobe Flash (formerly Macromedia). The software is aimed at animation on the web, and has become the most popular package, (Note that at this time, Flash is being phased out and replaced with HTML5.) mostly because it has a quick download time and is very robust.
There are many other animation tools on the market, but if you are considering a career in animation, it is worthwhile remembering that animation software is simply a tool to use, you need to know the basics of animation and design, and you will generally need good drawing skills - expertise in animation software is no substitute for these skills.
Make sure to also check out:
Computer Animation Schools
Animation Career Information
How to Become a 3D Modeler