SIGG Bottles for Kids
This is the ONLY truly leakproof bottle I have ever found for my kids. It wins on all fronts versus the many bottles I've bought from baby stores except a couple: it is pricey, its metal exterior is cold on the hands for cold drinks, and it is a bit tougher for young kids to use. The price covers itself when you realize how long the thing lasts and how useful it is. The cold on the hands part can be solved by buying the accessory handle.