I've been searching for good sippy cups for a long time. I was pretty happy with the Playtex brand cups until everyone started talking about BPA and wondering if their kids' sippies were safe. We still have a bunch of the Playtex ones, and they are very leak-proof and probably BPA free too, but I have found that the Nalgene Tritan Grip n' Gulp for kids are now my ultimate favorite.
Why I like them:
They are BPA free
Just like Nalgene's adult water bottles, which I have used for years, they are extremely durable...even when thrown against pavement by angry children
They aren't baby-ish, making them perfect for older kids too. Your child could use this cup from 12 months until 10 years old.
I can carry 3 sippy cups in one hand while I'm juggling kids or keys in the other, thanks to the little finger loop
They are completely leak-proof
Residue doesn't build up in them like it does in our Playtex cups
Easy to remove valve--and large enough that it's harder to lose
They hold 12 ounces, which means less fill-ups for our extremely thirsty kid
My "oral child" who chews everything to destruction has left tooth marks on her spout but hasn't managed to destroy it or smash it in--it's a very durable spout!
On the http://www.amazon.com/ reviews, some of the moms said their children couldn't get any liquid out of them. We haven't had this problem at all. It does take a bit more suction than our Playtex cups, but I count this as a blessing seeing as how it takes Jeremiah around 6 minutes to drain his 12 ounce Nalgene sippy instead of 1 minute (the length of time it takes him to drain his 10 ounce Playtex).
Some moms don't like that they have to tip the cup up to drink from it. If you prefer that your child not have to tip their cup up, you can give this sippy a try, which one of my mom-of-4-four-and-under friends highly recommends. I was going to buy this kind but couldn't bring myself to pay $20 per sippy, knowing my kids would probably lose them the next day if I did. Also, some moms said the straw pushed their kids' teeth forward so I wasn't sure I wanted them after all. Someday, when they go on a REALLY great sale I will try them and see if they become my new favorite.
You can buy the Nalgene Tritan Grip N' Gulp online from several different places, but ebay seems to have the lowest prices, even after shipping. They will run you around $8 each after shipping. Because a local sport and outdoor store here had them for $8 each, I purchased mine locally. It seems expensive, but I think they are worth EVERY penny. My kids have used them hundreds of times and they have been the best thing ever for soccer practices and games, picnics to the park or the mountains, church, taking into restaurants on our long trip to MN and back, and just drinking from all day long. And in spite of taking them everywhere we haven't lost one yet.....thankfully! They have 4 colors, which means whether or not we have a boy or girl the fourth child is going to end up with a pink one. Maybe.
One more thing: Most pics online show a sideview that leaves you wondering if they have a pointed spout that is uncomfortable for the child. The spout is not pointed, but rather very similar to the Playtex sippy spouts. This is a blurry shot of Justus' cup.