I think we should consider a few rules of thumb for determining our top 10:
Demonstrated skill - in other words, a combination of how the player has looked on the ice and the results (read: statistics) they've recorded
Upside - the player's potential, or how much greater you envision their skill set to be in the future, and how playable that will be in the NHL...frequently expressed as a "surefire 1st liner", or "top 6 forward", or "2nd-pairing defenceman", etc.
League Experience - This one should always be kept in mind. NHL > AHL = Europe > ECHL/OHL/WHL/QMJHL/USHL Great achievement at one level should always be kept in the context that it should not be equated with success at higher levels. Even with very basic league equivalencies employed, Bryan Little's 46 points was equivalent-to-better than any CHL player - and keep in mind we know Little is a competent player at evens, which we would not yet know about any given CHL player.
With that set of criteria in mind, here are my top 10 under 25 (age determined using the start of the season, October 13):
Evander Kane - Do I even need to explain?