Do you want CRT or LCD.
CRT is mostly 4:3, you have computer monitor CRT's up to 22 inch, and TV's also around 27 inch or bigger.
The largest 4:3 LCD are 21.3 inch panels by Samsung and LG, but they are laggy and expensive, so with LCD 4:3 the HP LP2065 is the best option (nice viewing angles for vertical mounting, quick response, no noticable lag).
If you want bigger, LCD is 16:10 or 16:9. The largest 4:3 image on an LCD monitor can be made with a HANNSG 28 inch 16:10 screen. Wanting larger means you should use 16:9 TV's.
Best large quality image LCD's (the HannsG is not that well made) are the LG W2600HP, the DELL 2709 or the DELL 2711.