128 x 192 Graphics on a TRS-80
I managed to get my stock TRS-80 Model 3 to display 128 x 192 full-screen graphics. The downside? It has an effective 15 frames per second update rate making it a bit flickery. I daresay impressive, nonetheless.
The other big problem is showing it off without a real TRS-80. Unless you're viewing this on an old CRT running at 60 Hz you won't get too close. I think these 4 images flipping past give a pretty good approximation and are about what you'd see running on the emulator.

Here's a picture I took with my cell phone. Pretty low quality but what's worse is the impression of a solid image. Notice the curve of the display tube.

This video capture on youtube really falls flat. At 30 FPS the effect is pretty much entirely lost.
George Phillips, June 30, 2009. george -at- 48k.ca