At iThemes Hosting we know that we can do two things very well. Provide phenomenal plugins for your site and provide a top of the line hosting experience. To that end, we also know what could be a drawback for us and that's hosting DNS. Thankfully, there are a large number of DNS providers that can handle that aspect for you! Below you'll find a few options to consider.
We recommend that you take a look at CloudFlare and their offerings which includes a free version that would cover most people needs! They also provide a number of added benefits such as DDoS protection and caching. You can find detailed information on how to set up your iThemes Hosting site to use CloudFlare for DNS by reviewing either their support documentation or ours!
Your Domain Registrar
Most domain registrars will also offer you the ability to utilize their DNS services and direct your website to whatever hosting provider it is that you are using. These tend to allow for the modification of A records, CNAMEs, MX, and other standard DNS functions. Your best source for how to set up DNS with your domain registrar is to seek out their support documentation. For the sake of setting up your iThemes hosting, you will want to look primarily for A record adjustments.
Alternative DNS Providers
Just as there are many hosting providers to choose from there are also a large number of DNS providers who will be able to help you manage your DNS needs. While we cannot keep up with the ever-growing number of providers if you find one you like.. use them! Thier support documentation should be able to help you get through the process of setting your sites A records to point to the IP we provide for you.