Forever 21 always has the most lively look books. The latest one features its newest activewear — spunky sports bras, striped stretch pants, short shorts, zip-up jackets, you get the picture. While it's nearly impossible to work out in heels — accident waiting to happen! — it's fun to imagine a world where exercising looks so damn sexy. The best part is the collection starts at $3.80. Since Alexander Wang made sports bras popular off the gym premises, consider getting one to pair underneath everyday tanks and tees.