I was going to make a top 5 'coolest moment TNG list'....but was only inspired by a couple, more will come to me.
1. The Defector: "Then you shall have it,... Mr. Worf?" (Three Klingon warships decloak)
2. Best of Both Worlds Part 1: The ending is the most memorable, but the return from station break in act one has the tension ratcheted to 11. "Captain. YOU are being hailed!"
edit: I wanted to include something from "Booby Trap", but I'm on this huge Ron Jones kick right now, and I think he's unduly affecting my selections.