SoftLayer's bare server API (http://softlayer.com/resources_api.html) and monthly pricing have suited our needs nicely. We've seen seen two problems (a porn site in the same datacenter sometimes gets DDOSed and the firewall in one data center is remarkably flaky), and they've been remarkably quick to respond to each.

The amount of tooling around the Amazon ecosystem is nice, but we mostly just use it for automating builds.