I would definitely recommend Rackspace. As part of my job I have dealt with them for several setups for both our own projects and projects. They're not kidding when they say that they have fanatical support, they've always been super responsive, given clear warnings about anything going on that might effect our service, and have proven extremely knowledgable. In addition to maintaining your server they are also very good at helping you grow and scale your enviroment as you need.

Rackspace is definitely not cheap but they are absolutely worth every penny and are perfectly targeted for your situation.

Sorry if this sounds like an ad but I truely have been amazed by my experiances with rackspace and will always recommend them to anybody in this situation.