aside from the obvious all-time greats and hall of famers, such as those mentioned above, and anyone from the last decade, which would be un-historical, here are some less well-remembered guys who had unbelievable runs--
henrik tallinder, 2006. not a coincidence that buffalo was up 2-1 when tallinder got hurt, and proceeded to lose the series 3-4. that buffalo defense was beyond decimated, finishing the series with tallinder, the puck-moving middle pair of numinnen-kalinin, and jay mckee all out. they were in game seven of the conference finals with four career AHLers: nathan paetsch, jeff jillson, doug janik, and the infamous rory fitzpatrick. tallinder was the guy who was holding it together, though. he and lydman were an unbelievable shutdown pair, and for a primarily defensive guy he provided some unlikely offense from the back end in the ottawa series (5 points in 5 games), to knock off the number one seed in the east.
marty mcsorley, 1993. somehow he put together a dominating two-way playoff run where he, not rob blake, not the hotshot rookies zhitnik and sydor (though zhitnik was also fantastic), not a still-steady charlie huddy, was far and away LA's best defenseman. i feel like in that era, when GMs kept picking future goons in hopes they'd develop into star power forwards (antoski, nazarov, you know), we never saw an al secord situation actually play out. but we did see something even more rare, which was mcsorley's star turn.
mark tinordi, 1991. another guy who hit a level of all-round game that he never touched again. maybe it was because it was bob gainey's team, maybe it was because bobby smith and doug jarvis and brian hayward were all there, but i remember distinctly hearing larry robinson comparisons and i think the temperature was definitely that tinordi had a big jump ahead of him.
keith carney, 2003. just a perfect storm of a player and the exact right coach coming together. carney didn't have to do anything offensively, he just was so smart at suppressing shots, breaking up the rush; i just remember thinking he was the perfect defensive player. the only other time i ever thought that was watching ryan suter in the 2011 series against vancouver. methodical, clockwork, and both guys were a lot stronger than they looked.
on the carney wavelength, scott hannan in 2004 was a defensive machine. cheap as hell, got away with all sorts of sneaky underhanded things, but also kind of the epitome of a blood and guts defender. another guy in that vein is dmitri yushkevich in 2000.
and a few rookies that i thought were destined for so much more. darius kasparaitis, 1993. if you said he would become a poor man's chelios, i wouldn't have blinked. ed jovanovski, 1994. so aggressive, but played so well within florida's system; in all those years in vancouver, i never saw jovo display 1/5 of the intelligence that he showed as a rookie a decade beyond his years in florida. maybe an indictment on marc crawford? and jordan leopold, 2004. that guy manned the point like he was larry murphy. what happened?