Ok, this would be my top 20, in no order:
1: C-55 Georges Vezina. Sure, there were sets before this one, but this is the grand-daddy of vintage cards
2: 1923/24 W.iIlliam Patterson Bert Corbeau - The most valuable single card bar none (sorry all you Sid Cup RC holders) and one of the very first SSP's or XSP or whatever you want to call it. The complete set of cards was redeemable for a prize and this was the toughie of the bunch
3: 1936/39 OPC Series D Howie Moernz - The pop-up cards make their debut, and vintage collectors to this day still pay premiums for anything from this set unpopped
4: 1951/52 Parkhurst The Winning Goal - Hockey's most memorable and tragic moment. It inspired a HOF card which inspired a tragically hip song.
5: 1951/52 Parkhurst Gordie Howe - One of the 2 most important players in the post-war, pre-Orr days
6: 1951/52 Parkhurst Rocket Richard - The man who transcended sports and became a cultural icon
7: 1954/55 Topps Gordie Howe - over 50 years later this is still one of the best designs in hockey.
8: 1955/56 Parkhurst Jacques Plante - A memorable shot of Plante making a glove-save during an era of rather pedestrian photos for hockey cards.
9: 1958/59 Topps Bobby Hull - The absolute definition of Condition Sensitive.
10: 1963/64 Parkhurst Gordie Howe - Howe posed infront of the star spangled banner is a classic
11: 1966/67 Topps Bobby Orr - A classic design, and one of the games 5 best players
12: 1972/73 OPC Phil Roberto - Fighting makes its debut on a hockey card
13: 1969/70 OPC Terry Sawchuk Memorial - The first of sadly a few cards dedicated to players taken before their time.
14: 1979/80 OPC Wayne Gretzky - One of the most reprinted cards of all time, and one that is on virtually every wantlist. Gretzky was the greatest player in hockey history, and this is his first card.
15: 1988/89 Topps Wayne Gretzky - An era ends and another begins as Gretzky dons the Kings Jersey
16: 1990/91 Pro Set Stanley Cup Hologram - The first "premium insert" card - This one was a needle in a haystack despite 10000 copies
17: 1990/91 UD French Sergei Fedorov - Speculation and perceived scarcity hit the hockey card market. This card once sold for hundreds, and people scooped them up by the gross in hopes of financing future education, house and car payments. When the hobby market crashed, no card crashed harder than this card.
18: 1992.93 UD Series 1 Eric Lindros - OPC had airbrushed heads over other bodies before, but this card caused a controversy when it hit, and rumours of it being an SP soon followed.
19: 1996/97 UD Game Jerseys - Memorabilia makes its first appearance on hockey cards. These cards still look fantastic and set a trend. Pick your favorite player (I'll go with Lemieux for this one)
20: 05/06 The Cup Sidney Crosby RC - A speculators and investory dream. This has every element of what collectors look for today (patch, autograph, serial numbering, etc) and regardless of whether its due to investors, hype, speculation, SIds on-ice play, celebrity status or whatever, it's the most significant card post-lockout.