Keeper of the Katra, by Chris Dickenson
It's eighteen years old, but for me, it's the only thing that justifies the existence of The Final Frontier. It is the most fascinating and pitch perfect piece of gen fic I read as a teenager, and believe me when I tell you that it still holds up years later. If you haven't read this novella already, go forth and do so without delay!
(Posted publicly for outside surfers.)
ETA: I just realized they're only doing SG1 fics at the above link. But hell, why can't we make this multifandom? There can never be too much gen, says I.