Learn Japanese | Tae Kim's Guide to Learning Japanese
A lot of people don't think very highly of it, but it's free. If you can't/won't use Genki or Minna no Nihongo textbooks, you could try it out.
There's also Welcome to IMABI! which covers much more. I haven't used it, so I can't really say much about it.
WEB版 エリンが挑戦！にほんごできます。｜Global Home
Run by the Japan Foundation, who are also responsible for the JLPT. Organised in a much more "textbook-like" fashion than a lot of the online stuff.