Moving player while jumping

I have my cube jumping around, but if he’s not moving before hand, he just jumps straight up and then back down. So how can I have it so that when you jump, you can still move side to side (left to right)if you have no starting velocity. I’m using a Character Controller, here’s my jumping code:

        if (Input.GetButton ("Jump")) {
            moveDirection.y = jumpSpeed;
        }
    }

    moveDirection.y -= gravity * Time.deltaTime;
    controller.Move(moveDirection * Time.deltaTime);

The problem isn’t in the part you’ve posted. It seems you’re using the example code in CharacterController.Move, where movement is controlled only when the character is grounded. You could move the control code outside this if, but this would kill the jump feature because the vertical velocity is always zeroed when reading the input axes. To get both things, you must keep the vertical velocity in a separate variable, like this:

var speed : float = 6.0;
var jumpSpeed : float = 8.0;
var gravity : float = 10.0;

private var moveDirection : Vector3 = Vector3.zero;
private var vertVel: float = 0; // vertical velocity 

function Update() {
    var controller : CharacterController = GetComponent(CharacterController);
    // read the controls outside the if:
    moveDirection = Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
    moveDirection = transform.TransformDirection(moveDirection) * speed;
    if (controller.isGrounded) { // if it's grounded...
        if (Input.GetButton ("Jump")) { // and Jump is pressed...
            vertVel = jumpSpeed; // vertical velocity = jumpSpeed
        }
    }
    vertVel -= gravity * Time.deltaTime; // apply gravity to the vertical velocity
    moveDirection.y = vertVel; // combine move direction with vertical velocity
    controller.Move(moveDirection * Time.deltaTime); // and Move
}