Second the
Doomsday Book rec. Marvelous and poignant. Willis' novella
Fire Watch set in the same universe also has that quality and is available to read free online, courtesy of Infinity Plus.
Another surefire tearjerker is Mike Resnick's award-winning Kirinyaga story "
For I Have Touched the Sky", readable online as a sample chapter from the DRM-free collection at Baen's Webscriptions.
And from Lois McMaster Bujold's Vorkosigan saga, I'd add
Mirror Dance and
Memory, in which you get to see two men essentially destroyed and rebuilt from the ground up. Mind you, the effect works better if you've read the previous books, though the other recs above are standalone.