I highly recommend the Safe Sippy 2. It's an easy way to keep dangerous toxins out of your kids water. We all know the dangers of BPA, so now they make BPA free plastic, which is great, but unfortunately even the BPA free plastics still contain other hazardous chemicals that leech into our water and can disrupt our hormones.
You can buy it on Amazon or at Whole Foods.
It converts from a sippy to a straw, which makes it a cup that can last a long time to justify paying $15 for one cup.