In my experience, Linode is the best roll-your-own you-are-on-your-own cloud provider. Obviously they are aimed at the savvy but it's reliable, cheap while being easy to estimate costs, simple to configure and expand, pretty good documentation, plus it doesn't have the learning curve or linguistic peculiarities of Amazon.

Regarding Rackspace, I've had good experience with them when working at mid-size and larger companies. Unfortunately I've had the opposite experience when functioning as a freelancer, working with startups, or as an entrepreneur myself. Rackspace didn't even respond to sales inquiries. Initially I figured this was a strangely repeated fluke, but other small companies and entrepreneurs I've spoken to have reported the exact same thing, where they send an inquiry to Rackspace or ask to speak with a sales engineer, and they get no response. Nothing, zip, nada. I find that very strange, and am speculating RS no longer wants to deal with the growing pains and frequent support requests of startups, but it certainly makes the decision to stick with Linode or EC2 much easier.

I don't have much experience with dedicated anymore, but have repeatedly heard good things about ServInt and SingleHop. Have also heard good things about Firehost for a managed cloud provider. I would love to hear others opinion and experience on any of the aforementioned companies though.