Back in the days of the Bloodstone modules, there was a room with a Tarrasque in it. (No, really.) My Wizard had a Wand of Force. I put up a Wall of Force, leaving a tiny bit of clearance on one side (though which the massive beastie could not fit, but we could toss spells). The Illusionist threw Chromatic Orbs at it until it failed a save and died. I re-absorbed the Wall of Force into the Wand (didn't even waste a charge!) and we proceeded past the temporarily dead Tarrasque. Later in the adventure, a wrong choice sends you to the beginning, and we ended up in that room again. The DM just said, 'fine, you kill it again, next room.'
We also had the bug-on-windshield effect on a dragon with a Wall of Force in another game. Kinda anticlimactic. That was a GURPS game, and the spell was Force Dome, but the effect was identical to what it would have been in AD&D.
The best dragon-kill was in Return to the Temple of Elemental Evil, I think. A dragon was attacking us in a temple complex, zipping in and out of tunnels to flyby attack us in a central chamber. He was breathing for insane amounts of damage, given his size, and one of the characters noted that he was far too small, able to fit easily in these tunnels, when he should have been much bigger. Spotting a bracer looking bit of jewelry on his forelimb, the Cleric of Wee Jas, who had held an action for his next flyby, threw a targetted Dispel Magic on it, and, as luck would have it, turned off his magic item of Reduce Person while he was still in the tunnel. Instant death by squishage. On the downside, we needed to go that way, and it took the Druid Summoning a Thoqqua to make us a tunnel around the dead, squished dragon blocking our path...