My wife is getting into photography and is doing her first wedding this month for a family member. She has a Canon Rebel xti and only has the lenses that came with it. I want to surprise her with a good lense and have no idea what to get. I don't want to spen more than around 500 dollars or so. I want something that will be good for the wedding but that she will like for the future as well. What do you suggest? Thank you so much!