Be sure to check out: http://www.chiffandfipple.com

They have reviews of both cheap and expensive whistles to buy. They also have a lot of great advice.

Clarks are traditional with a wooden wedge and usually they all play just fine. I've played 30 or so in either C or D and enver found a bad one.

Generations with the plastic mouthpiece are good too, but they definately have some quality control problems. I bought a set of 6 in different keys last year and 2 of them are not nearly as good as the other four.