Being an IT guy and a student of Japanese, I'm expectedly a fan of using software to study. I've tried just about every type of Japanese learning software there is, so here I've compiled a list of my favorites:
The Rosetta Stone (PC / Mac) - www.rosettastone.com
The Rosetta Stone is the Ferrari of language learning software. It's fun and extremely interactive, engaging all the senses to maximize retention. It's automatic lesson review feature quizzes like a real teacher, and it's the only software I've ever found that supports voice recognition, making speaking practice possible. It's by far the software that comes closest to classroom learning.