Just a cheap-o 21" Sylvania connected via S-Video. Not great, but it works well enough when I need my vert fix. For DC stuff, I use a VGA monitor instead.
Samsung SyncMaster 570V...I think it came with my computer. Since I only have a vga box for my DC I use a 32" Phillips tv just out of the frame to play ps2 on....tate'd it many times without problem. Bonus points if you can identify all the sega cd games.
Most of the time I use my Commodore 1084 for both Yoko and Tate with a Matt-made RGB cable, though sometimes I'll hook something (usually my SNES) up to my dad's TV (it's somewhere between 25-30 inches) via regular ol' AV cables, though I only use that for Yoko.
Rotates on its stand, and it's great for MAME, less so for console shmups because it doesn't rotate the right way. It can be removed from the base though, and is light enough to handle easily.
I have a PVM-2530 (thanks, Wanderer) for PS2 and Supergun stuff, and a 20" Aquos TV on a swivel for High Res stuff.... my wife had an operation so it's in her room now. PVM for everything at the moment.