I know these may look like something Madonna might wear on stage, but they're actually used to help with Aunt Flo. These menstrual cups are an eco-friendly alternative to tampons that are BPA-free, and because they're made of nonabsorbent material, they reduce your risk of toxic shock syndrome.
The Keeper ($35) on the right is made of natural rubber, so if you have a latex allergy, go for the Diva Cup ($33), which is made of silicone. Both are reusable and can be worn up to 12 hours, so compared to feminine hygiene products, you might find this to be more convenient and comfortable when exercising.
Source: Flickr User Greencolander