Price Paid: $9
Bought the green one for my son in 2008 (he was one) and it was hands down the best "sippy" cup we have come across. Does not leak, replacement valves are cheap, and the wide mouth accepts regular 1L Nalgene loop-top bottle lids for when the child grows out of the sippy lid.
We have only ever filled it with water so I have no idea if it retains flavors. Shaped so that a child can grip it easily. It is very rugged, ours has withstood many falls and tumbles. Our son is now almost four and still loves his.
Some of the replacement valves did not allow a decent flow of water. This is easily remedied by removing the valve and gently enlarging the X shaped slit with a sharp knife. I have also heard that people have had a similar problem with the valves in a new bottle. Really easy to fix.