I think having VPS is the best choice for you but where that is the other thing. If you're generally O'k with GoDaddy stick to it. You know you may have issues with the other hosts too. It occurs from time to time with every hosts.
You might have a hard time to find a provider that has a prebuilt plan for the amount of bandwidth you are looking at. You might want to look at providers that offer a custom plan (you probably can email some providers, if they don't offer it on their site). Since I'm not sure what kind of site you are running (Forums, etc) and what kind of software you are using (vB, phpBB, drupal, etc), I couldn't really give an accurate estimate for the amount of RAM. For disk, you might want to get 10GB so you have enough room for the Operating System, plus, room to expand. For $100, depending on provider, you can probably get 10GB of disk, 256MB of RAM, and 800GB or so of transfer. You will probably want to look for a webhost that offers low bandwidth overages, so, if you *do* go over, it won't break the bank. Hopes this helps!
Aah, I haven't tried Joomla, but, I've had experience with Drupal, and, it seems to scale really well. I suggest you add a PHP accelerator to your site, it can really make a *huge* difference. I've used eAccelerator before, and, it works really well for me. You could try moving stuff over to lighttpd, to get more performance for your dollar. But, I would suggest least 192MB of ram for those sites.