Some of the tools I find most useful are these:

The Adobe Creative Suite provides a powerful set of tools for image maniimpulation, illustration and diagramming, and document preparation, publication and sharing.

Luxology's modo is a powerful 3D modeling tool that allows detailed examination of form and construction elements throughout the design process. Its powerful visualization capability helps with understanding and communicating the experience of a building or design.

Autodesk Revit offers flexible and powerful parametric design tools for architects. It is also well integrated with structural and MEP design. As a fully-fledged Building Information Modeling (BIM) solution, it ensures consistency through all the views of a building. Its 3D modeling capabilities are supported by a rich constraint management system that establishes and maintains relationships between elements of the design, increasing productivity and reducing errors.

Graphisoft's ArchiCAD is a well-tested and mature BIM application. Because it works directly with the elements of a building (walls, floors, roof, window and door elements etc.), and because it models directly in three dimensions, it is easy and efficient to develop practical (i.e. buildable) solutions to design challenges. Running on the Mac and PC, it also supports collaborative team design, which is the norm with today's complex projects.