I love the under armour one. it has two pieces. so it's easier to pull the bottom down when you want to.

http://www.underarmour.com/shop/wome...od/8000022-400

I found it for $25 at D I C K' s. but last time I was there I found one that was made my Nike in the lightweight sphere fabric for $20. It's the same style but i like it better.