Definitely no strings unless you are there to supervise! But you can buy toys that are like a ribbon on the end of a wand that you move around for your cat to play with. These are great!
The cat dancer is definitely a great toy.
One thing to do is get a bunch of different toys - different kinds of balls, mice, furry things, etc. But only give her a few at a time. Keep a shoebox in the closet and at any given time, keep most of her toys in there. Just rotate them every few days or once a week. That way they will seem new and more fun to her and you won't constantly have to buy new toys.

And don't forget about fun things you already have around the house. One of my cats will play with a crumpled ball of paper for hours, and another goes nuts for empty toilet paper rolls. The plastic rings from milk cartons are always a hit, too, as are twist ties (just supervise playtime with these).
An empty paper bag (with handles cut or removed, if applicable) can also provide hours of fun.