I don't know of any good resources on the internet. If you go to a used bookstore (or Amazon) you may be able to find good textbooks on the cheap; for my language study I always use several texts in conjunction, and I have found the best Arabic textbooks to be Al Kitaab (more inductive) and Elementary Modern Standard Arabic (very dry and grammar-heavy, but rich). Teach Yourself is, suprisingly, not all that bad, but I would only use it as a supplement. You might also look at the Hippocrene 'Beginner' series, which generally puts out good titles, and the Colloquial book; neither of which have I used myself, as a disclaimer. Unfortunately, textbooks are expensive, but they are a one-time investment that will last you a long time (all of the above are for MSA; finding good cheap dialect resources would be even cheaper). Past the intermediate level, of course, your best bet is a course or a native speaker friend (cheapest resource of all!). Beyond that, I'm afraid I can't help you (not being at an advanced level yet myself).