Good sippy cups for toddlers are rugged enough to take endless abuse, including constant chewing by practicing teeth, abandonment on the backseats of cars and within couch cushions, and regular bashings.
The Kid Basix Safe Sippy (*MSRP $11) is described as a cup that can outlast toddlerhood, with an ultra-sturdy stainless-steel bottle that will not leach chemicals into your child's water. The hard-spout lid made of BPA-free plastic is virtually chew-proof and replaceable if it gets damaged. Used with the sippy valve, the Safe Sippy also doesn't leak. But the straw adapter valve, which comes on the Safe Sippy 2 (*MSRP $16) , will leak if tipped on its side or turned upside down. The Safe Sippy straw adapter kit, which can be used on the basic Safe Sippy cup, comes with a stopper valve to seal the cup during travel.
The Tommee Tippee Explora Truly Spill Proof Trainer (*MSRP $16 for two) lives up to its name. A physicist helped design the lid to provide on-demand flow of fluid without leaking -- ever. For the most part, Tommee Tippee's claims seem to bear out. One parent tester reported throwing the Tommee Tippee cup out of a second story window to test for leaking, and it did not leak or break. However, Tommee Tippee cups are so difficult to assemble that most parents say they can only figure it out by watching an online video. There are also more pieces to wash.
Older toddlers, even though they still need the spill-proof properties of a sippy cup, may balk at the babyish sippy. These two well-reviewed cups look like something older siblings or mom and dad would use -- but they're still spill-proof.
Constructed of tough, BPA-free plastic, the Nalgene Grip 'n Gulp (*MSRP $9) can survive being driven over by a pickup truck and years of constant washing and use. One parent attests that it takes a couple of years for kid teeth to make a dent on the hard spout. The Grip 'n Gulp is totally leakproof as long as the valve is placed tightly inside the lid; the three pieces of the cup make it easy to use. It's also compatible with Nalgene's classic screw top, meaning it will last into adulthood.
The Playtex Coolster Tumbler Cup (*MSRP $6) is recommended for kids as young as 2, but it looks more like a grown-up cup because it lacks the hallmark sippy spout. It's also compatible with all lids in the Playtex line, so it can be a sippy or straw cup as well. Best of all -- it comes with a "Spill-Proof, Leak-Proof, and Break-Proof" money-back guarantee.