GravityTurn
This is a Kerbal Space Program plugin that will auto-pilot most crafts to a nearly maximum efficiency gravity turn launch.
The autopilot will launch to a given speed, initiate a slight turn, and follow the course of that turn all the way to a low orbit. Mostly this involves adjusting the throttle to keep the curvature of the orbit ascending to the desired prograde.
The plugin will handle staging as well as it can. Several parameters are adjustable to fine tune a launch to a particular vehicle. But the default parameters are usually enough to get to orbit using about 3300 m/s of delta-V or less.