I've been looking for a good solution for Arabic web fonts for while now and have been hitting my head against the wall with the lack of options available to me or the cost of buying a font and hosting it myself.
Just as I was contemplating making my own arabic font (no easy feat) it would seam that some of web services are beginning to add some decent options. Since I use Typekit I would prefer this to be the service with the Arabic fonts, but at the time of writing this isn't the case. This currently means that I would need to get a subscription to one or more of these, but hopefully it means that a change is coming across all the services so hopefully Typekit is right behind the others.
Here is a list of services with Arabic web fonts
Google has it's Early Access (Beta) list. Along side Arabic web fonts it also includes Korean, Thai, Tamil and Hindi.