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.
Webink has a few font that seem to look quite nice.
Font deck only has the one font currently.
Font.com has a massive amount of fonts. I'm 100% sure of the availability of the arabic fonts on the lower subscription tiers though.
As I find more services and test them out I will add to this list, but at least there are better options every day. Any tip offs, or services that you can share are always welcome below or on Twitter