"A Hundred Days".
One of the more solemn episodes of SG-1 that managed to show facets of O'Neill's character that were, sadly, not portrayed often throughout the series.
Written by a woman no less, which helped bring some resonance to his female consort.
Sigh, I miss the days of good sci-fi on television. At the present moment there is seemingly nothing to latch on to and that will not be cancelled in a matter of weeks.