The Logitech F710 Game controller makes a good remote control. From time to time it is necessary to manually control a robot: turning it on an off remotely, putting it into position for tests, activating certain hardware and/or software modules. It is quite expensive (around $AU65 on eBay), but has a good range, is high quality and seems quite reliable.
There are many robot videos where the robot is controlled by a the kind of remote control which is used for remote control aircraft or boats. In fact the Sabertooth motor controller has an interface which can plug directly into the PWM-style receiver for one of these, but if you run a robot with a PWM remote control, you have really just built a remote controlled car. If that is the aim, then no problem, but if the goal is autonomy, then it has to take commands via a software program.
The software program might be a simple as reading the (X, Y) coordinates from the joystick and issuing
setSabertoothSpeed(LEFT_MOTOR, Y + X);
setSabertoothSpeed(RIGHT_MOTOR, Y - X);