Moving to the Cloud – Any Good Cloud Solutions for State Government?

Our state agency is finally ready to move some of our older systems to the cloud, but we're worried about security, costs, and keeping control of our data. We're looking at different cloud solutions for state government and trying to figure out which providers understand our unique rules. Has anyone successfully migrated using cloud solutions for state government? Which vendors made the process smooth, and how did you keep costs from spiraling out of control after the move?