I'd have to give my vote to a number of players from last year to this year. Erik Fabian has really stepped up this year as a leader on the team. A grinder who doesn't score many points, he took charge of the team last spring in that memorable run and left off this year all season long giving 100% on every single shift, mucking it up in the corners, banging away with opposing players, blocking shots, and forechecking extremely hard.
Rylan Kaip, another great example of hard work and positive attitude. Last year he was sidelined with the post-concussion syndrome, never really got an opportunity to get into a groove and had a great attitude and work ethic all season long this year. He created numerous chances, but the puck just seemed to defy him and never went in. He finally was rewarded at the WCHA Final Five with two HUGE goals to help come back to defeat the Badgers!!! He's made some great passes to teammates for goals, scored a couple goals now, has had some awesome chances to score and hit posts or crossbars, even got denied on a penalty shot.
Matt Smaby is an example of true leadership and experience at this level. He really helped those young D come into their own, he's brought along all the freshmen D to the level needed for competing night in and night out in the toughest conference in the country. He has really impacted some games with bone-crushing checks, he leads by example. He works hard, helps out on the power play, does some penalty killing, blocks shots, takes on opposing teams' best players and gives the team an adrenaline rush with his play on defense.
I can't think of any other players who've improved as greatly as Fabian, Kaip or Smaby in my mind unless someone gives a solid explanation to change my mind. That is why these three greats will have my vote for now.