Monitors that are 19" and 22" just do have TN panels which are a lot cheaper, not so good viewing angles if you're watching a film and the colour can band easily. The dot pitch is higher too, meaning on a 20 and a 22" inch you're both at the resolution 1680x1050, so can you see that the 22" won't be as sharp because it's putting the same pixels on a bigger screen.
I'd either go for a PVA panel in the 20" category, or save up a few pennies and go for a super PVA panel in the 24" screen size, there is also the OcUK DGM monitor that has a good panel but not so good build quality that you'll see in the top right hand corner of the forums advertised that's a good buy.
Whatever you choose you'll definitely see an improvement, just if you get a 22" TN and ever have it side by side with a 20/24" screen, you'll see your inferiorities.