This thread is for discussing the Japanese language and getting study resources for it.
I'll link to some good sites for different topics, including particles, grammar and vocab building.
First things first, if you don't know how to read Hiragana, it's the first thing you should learn. All resources I'm going to link use Hiragana.
Tofugu is always a very good source of Japanese learning resources. Its articles are very helpful, so if you want to learn something that isn't here (like foreign words that are used in Japanese), go there.
NIHONGO eな has a variety of links to different resources categorized by what they're for (reading, culture, writing, listening, etc.)
Tae Kim's Guide to Learning Japanese is a great site, too.
[size=large]Hiragana and Katakana[/size]
As usual, Tofugu provides good tools for studying Hiragana and Katakana:
Hiragana
Katakana
Once you know them moderately well, it's time to practice. Obenkyo is an android app that has quizzes for Katakana, Hiragana and goes all the way up to Kanji. It even has some grammar explanations that are pretty nifty, so I'd recommend getting it. For computer resources, here are some links (they're not very many as most hiragana quiz sites are pretty bullshitty):
http://www.hiraganaquiz.com/
http://learnjapanesepod.com/kana-invaders/
http://www.kongregate.com/games/tukkun/kana-warrior This last one's a bit silly, but it's good.
For kanji, I´d say the best resource is definitely WaniKani. The first 3 levels are free, and everything after that is currently $8/month or $80/year. Once it comes out of beta this Sebtember, though, its price will be kicked up to $10/month and $100/year. For obvious reasons, this isn't the best option for college students and the like, so if you want a free alternative, I've heard Memrise is good too. I haven't used it, but you could give it a shot.
[size=large]Particles and Grammar[/size]
GreenWarrior's grammar guides on WaniKani 1-5
These grammar guides are incredibly extensive and may seem overwhelming, but they're well explained and can walk you through the grammar in Japanese excellently.
1- https://www.wanikani.com/chat/kanji-and-japanese/7113
2- https://www.wanikani.com/chat/kanji-and-japanese/7230
3- https://www.wanikani.com/chat/kanji-and-japanese/7292
4- https://www.wanikani.com/chat/kanji-and-japanese/7750
5- https://www.wanikani.com/chat/kanji-and-japanese/8142
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In-depth comparison of は and が
This is the best explanation I've read for differentiating these to. They're incredibly nuanced, but understanding the difference between them is a key to fluency.
http://nihonshock.com/2010/02/particles-the-difference-between-wa-and-ga/
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General grammar books
Tofugu sings this trilogy's praises often, so I might as well link it here. Basic, Intermediate and Advanced.
[size=large]Vocabulary Building and Practice[/size]
WaniKani has vocabulary lessons among its Kanji ones, so it´s a good way to build it up. delvinlanguage.com is probably the coolest way to build up vocab and practice hearing. It takes video clips from Japanese Soap Operas, Japanese Ads, and Ghibli Movies, and asks you to write down words they said and their meaning. If you want to practice writing, Lang8 is a site where you can write in Japanese and a native speaker will correct you.
If you want to learn Japanese effectively through anime, once you've learned a fair share of Kanji you can use kitsunekko.net has Japanese subs up for download. That way you can listen to Japanese while practicing reading.
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(This post is a work in progress)
EDIT: This post has reached a hump. If you have any sites you'd like me to add, please let me know so I can expand on it.