In the mainstream consumer channel there's only 23"+ wide aspect panels that allow you to display 1080p with 1:1 pixel mapping. The 20-22" don't quite make it, typically running 1680x1050 without the 1:1 option.
A few of the panels that will do 1:1 @ 1080p include:
Dell 2407WFP REV A04 only
BenQ FP241W (with update), VW and WZ
Gateway FP2485W
There's a few others but they're $1000+ along with some recently announced but not yet available 24" panels.