This thread is old... But I'd recommend iStart Japanese by Mirai Language Systems.
It has a vocabulary list, quizzes, and lessons that take only a few minutes. I've had it for about a week now and I can now say things like "I eat sushi", "Do you read manga?", "Won't you have some coffee?", "Beautiful car", "I like it", "I like this, so I'll buy it", "Let's stay home and watch a movie", "I have a dog", etc. I know it all by memory and the lessons are fantastic, I've got full points on every quiz so far.
It also teaches you to read and write hiragana and katakana. I'm focusing on my spoken Japanese at the moment so I can't speak for effectiveness there, but investing in a couple of good books like the DK Japaneses-English Visual Bilingual Dictionary and Tuttle's Japanese Hiragana & Katakana for Beginners will help you along. I bought both of those books about a week back and they're fantastic - the iStart app teaches you basic sentence structure, and then you just have to replace a word or two to say something else.
The app teaches you that "I eat sushi" is "Sushi-o tabemasu".
But the dictionary I have expands my vocab, so I can say "Pan-o tabemasu" - that is, "I eat bread".
Good luck! :3