Here ya go...
http://www.thewhistleshop.com/catalog/sets/Clarke/clarke.htm
Seriously. It helps if you're into traditional Irish music, but it isn't essential. Pennywhistle is fun, and fairly easy to play. It's also a rare instance of getting more than you pay for. You can have a professional instrument for less than $10.
The above site looks low budget, but I can personally vouch for them. It's been awhile, but I've bought numerous whistles from them in the past. The set I linked is a great starter set, and has some fun to play music in it.