I don't know if I've already mentioned these elsewhere, but...
One that I fondly recall was when I was coming out of the Kings Row Wentworth's. I realized that there was a commotion going on, centered on the roof of the three-story building across the street to the north of Wenty's - the rooftop where the Clockwork were always building something. There were three or four Crey there, about level 40 (I distinctly remember that at least one was an ice tank). Apparently, some high-level had outrun an ambush, and they were one-shotting any lowbie that got too close - especially innocent passers-by who didn't know what was going on. I don't know how many were blown out of the sky. That went on for about 10-15 minutes, with me wishing that I had a high-enough toon to go get, to do something about it. Then, from the north, a hero flew in, and started taking them down, one after another. It was just like watching a superhero work, and we lowbies were cheering him on. (Did the devs ever fix it so that an abandoned ambush de-spawned after a while, or when the ambush target zoned, or something?)
Another incident (not so fondly remembered) was also in KR. I was in front of the hospital, going southwest to a mission door, when I saw a huge swarm of Clockwork in front of me, running to the northeast, right at me - and I mean LOTS of them. I knew that I couldn't take them, so I ducked into the hospital to get out of their way. There were enough of them that they must have overwhelmed the police drones, and some of them FOLLOWED ME INTO THE HOSPITAL LOBBY! Few things in the game surprised me as much as when those doors opened. It took me a few seconds of "That's not possible!" before I could gather my wits and start counterattacking.
Man, I miss this game.