22. Is That Tasha?
Episode: Redemption (4.26)
The first half of Redemption is a pretty decent foray into Klingon/Romulan politics, and we think the cliffhanger is that Worf is resigning his commission to join the Klingon Civil War. But then we get slammed with the real cliffhanger.
21. Tapestry
Episode: Tapestry (6.15)
Seeing Picard change his past and wind up as a weaker version of himself is fun and heartbreaking. The final scene, where Picard recounts his near-death adventure from Q with Riker, is incredibly poignant.
Death By Troggles 
It would have been cheesy in the hands of a lessor actor, but Stewart makes that ending brilliant.