I've been self-studying Arabic for a long time, and have consequently come across many great sites and sources for Arabic learning materials. This is meant to be a list of the best online resources for how I learn Arabic. If you have any suggestions, feel free to comment below.
The Arabic alphabet
Shariah Program A very detailed and thorough guide to learning the alphabet.
Assimil Arabic with ease Assimil is my favorite beginners course in any language. This course teaches the alphabet in a gradual and intuitive way along with a lot of vocabulary and contextual grammar. If you're going to buy just one book for your Arabic studies, pick this one. (with audio) see my review of Assimil Arabic
My guide to deciphering Arabic handwriting This is a resource that I've made myself where I analyze a few examples of handwritten Arabic text, and synthesize it into a few general tendencies that you need to recognize in order to read the text as written by hand.
If you wish to delve further into the subject of Arabic Handwriting, I strongly recommend the book “Mastering Arabic Script” by Mahmood Gafaar and Jane Wightwick which is a great introduction to the alphabet in its printed as well as handwritten form.
Hindawi An archive of hundreds of e-books that you can download for free. The books are categorized into different subjects, including classics by the Egyptian Nobel prize winning author, Taha Hussein and a section of easy classics translated into Arabic
A tip for searching for Arabic books in word format (unless you have no problem with scanned pdf's) is looking up the books Wikipedia page, changing the language to Arabic and googling the Arabic title, or the Arabic spelling of the Author's name along with "filetype:doc" - example: اجاثا كريستي filetype:doc , for books by Agatha Christie. (I recommend you read "And then there were none")
Films and TV
7 great TV-shows in MSA - A list of 7 TV-shows in Modern Standard Arabic made available on YouTube for free by their individual production companies. Each series has 30 episodes and they're all in MSA (or Fusha) and made to a high standard.
Translated articles from the Arab world Articles from various media sources presented in English with a link back to the original source.
Sciware A great podcast by Dr. Mohamed Qasem, a Saudi university professor speaking about interesting scientific topics. What is especially great about this podcast is that it has transcripts of all of its episodes available. Something that's hard to find in Arabic.
RTVE Emisión en árabe An Arabic podcast by a Spanish radio station with a focus on culture and sports. If you enjoy Spanish culture and traditional music, this is definitely a must for you!
BBC Arabic An Arabic radio podcast from a British Perspective
SBS Arabic24 An Australian podcast with a lot of listeners calling in speaking their own dialect. The show deals with many current affairs and subjects that might influence Arabs living in Australia
Fuzzy Arabic Dictionary A dictionary powered by Yamli, that lets you look up words without knowing their exact spelling in Arabic
Almaany A great dictionary that translates from English to Arabic and the other way around
Google translate Well, good old Google hardly needs mentioning, but I use it more than anything else. A useful feature is pasting an URL into the text field, getting a complete translated and browse able version of any given website.
Five College's Arabic section This is a true treasure trove of interviews and dialogues along with their transcripts and translations in many dialects of Arabic. The site also provides resources for many other languages. Go check it out!
I personally had a list of over 350 words and phrases translated and recorded into Algerian Arabic (or Derja).
Other useful tools
Arabic Normalizer A handy little piece of software that removed all diacritics, vowels and accents from your text. This can be useful if you want to import the text into a system that doesn't handle diacritics well, like LingQ
Calibre Among other things, Calibre is good for converting epub or other e-book formats to other types of text, easier editable on your computer
That's it for now - Do you have an idea of something that I absolutely ought to add to this list? Please to post a link in the comments!