Here is a list of my favorite Arabic learning resources, both books and on the web.
At the outset, I'd like to state that, in my opinion, there are no 'good' online dictionaries for Arabic. Yes, there are some functional, convenient ones, but the best Arabic - English Dictionaries exist in print.
Google Translate is below average in quality but extremely convenient. Arabic is too complex a language to rely on a translation tool that will give you, in most instances, only one definition per term. It's even worse when translating sentences and is bad at recognizing rare or archaic vocabulary (and Classical Arabic is frequently invoked in intellectual and literary writings). But, that said, it's terrifically convenient. Best used when reading the news. You can also create lists, which is helps in studying vocabulary.
Dictionary Sakhr is a better choice that Google Translate and for the most part is adequate, though still problematic. You can only look up one term at a time, and like a print dictionary, you can't look up plural nouns or conjugated verbs (which you can plug into Google directly). An important advantage over Google is that Dictionary Sakhr gives you multiple definitions per term, which can be very helpful. But it's best to cross reference these with a print dictionary. Sometimes terms that appear to be synonyms are only vaguely related.
General Language Learning
Aswaat Arabiyya is a great service run by the University of Texas which offers free Arabic language videos at various proficiency levels. I was introduced to this website while studying at Rice, and it's been a big help. It has some great features to help you improve your listening proficiency. Many of the videos at the beginning levels include comprehension questions and exercises. You also have the ability to play the videos at slower than full-speed, which can help when first listening to the upper level videos. Best of all it's free!
GLOSS or the Global Online Language Support System is a service run by the U.S. Department of Defense and features comprehensive online language support for learners of various critical languages. The lessons in GLOSS are more comprehensive than those offered by Aswaat Arabiyya, including written and listening activities at all levels of the U.S. Government proficiency scale. Additionally, it features lessons in a variety of Arabic dialects, which can be of great benefit to students who mainly study Modern Standard Arabic. Like Aswaat Arabiyya, all GLOSS lessons are free!
An Introduction to Koranic and Classical Arabic by Wheeler Thackston
A very intense, very dense book, but the way that I first learned Arabic. It's not a language textbook like many are familiar with, but it is unparalleled in the way it prepares students to handle the intricacies of Arabic grammar and syntax. This is for very serious students only and is probably too overwhelming to be used without a teacher (just read a few pages and you'll see!)
Media Arabic by Alaa Elgibali and Nevenka Korica
I studied this book by myself in my fourth year of Arabic study and found it very accessible and beneficial to my comprehension of Arabic Media. There are a lot of Media books out there, but what I like about this one are how the exercises prepare you very well for understand the format and style of news articles and broadcasts. An acquaintance of mine criticizes it for being too easy, but I think it's a good fundamental approach of Arabic Media.