I'm currently test driving Digital Ocean, ServGrid, and Linode.

Digitial Ocean makes provisioning new servers incredibly easy (as does Linode). The process is near instant. Scaling a server up and down is also near instant, especially compared to Rackspace (it took over an hour the last time I scaled a server down with them).

But their network has proven the least reliable (I'm in their NY DC). My site monitors have reported a few outages, anywhere from 1 - 6 minutes a piece. By comparison, ServGrid and Linode haven't had any outages during my trial.

But their customer support is really fast, and I love the documentation and community they have around their offerings. I really wish they had a Dallas DC though.