FlxTween can be used to change values over time following a number of available curve functions.

Using tween allows you to pass any kind of object, and several parameters that you want to tween over.

// create a tween
FlxTween.tween(myObject, {parameter: destinationValue}, duration, {type: tweenType, easing: FlxEase: easeFunction});

Demonstration

package;

import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;
import flixel.tweens.FlxEase;
import flixel.tweens.FlxTween;

class PlayState extends FlxState
{
	var sprite:FlxSprite;
	
	override function create()
	{
		super.create();
		
		sprite = new FlxSprite("assets/sprite.png");
		sprite.x = sprite.y = 50;
		add(sprite);
		
		FlxTween.tween(sprite, {x: FlxG.width - sprite.width - 50, y: FlxG.height - sprite.height - 50, angle: 360}, 3,
			{type: FlxTweenType.PINGPONG, ease: FlxEase.sineInOut});
	}
}