I was curious, so I looked at the past 15 drafts to see what sort of late round picks (after 3rd) were impact players (top-6 F, top-4 D, 1G, elite bottom-6er).
2003
Matt Moulsen, W, NCAA
Jaro Halak, G, Slovak Jrs.
Dustin Bufflin, D/W, WHL
Toby Enstrom, D, Swe
Joe Pavelski, C, USHL (college bound)
Europe - 2, CHL - 1, NCAA (or bound) - 2
2004
Mark Streit, D, Swiss
Pekka Rinne, G, Fin
Troy Brouwer, W (*ducks*), WHL
Czech Roman Polak, D, Czech
Mikhail Grabovski, F, Russia
Kris Versteeg, W, WHL
Ryan Callahan, W, OHL
Europe - 4, CHL - 3, NCAA - O
2005
Patric Hornqvist, W, Swe
Anton Stralman, D, Swe
Darren Helm, F, WHL
Niklas Hjalmarsson, D, Swe
Keith Yandle, D, USHS
Europe -3 , CHL - 2, USHS - 1
2006
Matthieu Perreault, C, QMJHL
CHL - 1 (yikes, this was a bad late draft)
2007
Justin Braun, D, NCAA
Carl Gunnarson, D, Swe
Jake Muzzin, D, OHL
Jamie Benn, W, BCHL
Europe - 1. CHL - 1, NCAA -1, BCHL - 1
2008
Jason Demers, D, QMJHL
Cam Atkinson, F, USHS (NCAA bound)
Jared Spurgeon, D, WHL
Gustav Nyqusit, F, Swe
TJ Brodie, D, OHL
Braden Holtby, G, WHL
Europe - 1, CHL - 4, NCAA - 1
(Continued in a new post)