Rosetta Stone Online
Rosetta Stone German is one of the best programs to learn German at the computer.   The core of this program is word and image association, which is a powerful teaching method. It is a fun, interesting approach to learning the German language.

Power-Glide
Power-Glide German is an interactive, age-based language course that makes learning fun, fast and effective.  The program is a blend of the best innovations based on up-to-date understanding of linguistics and learning psychology.