That old Dell of your used an S-IPS panel, and you will surely going to disappoint in both color and view angles if you buy something with an el cheapo TN panel. Sorry to say this but $240 per isn't going to cut it! You need to spend a little more money!
And going to something like a 22" with resolution a LOWER resolution than you Dell's might make you cringe too. You Dell has resolution of 1600 x 1200 right? So if you want higher resolution, a 22" isn't going to cut it.
If it were me, the only format that makes sense is to get dual 24" IPS or PVA based panel, but preferably IPS based, like the HP LP2475w! Price will be an issue though. I have these following Dell monitors right now, the Dell 20" 2008WFP (S-IPS panel), 24" 2408WFP (PVA panel), and 22" 2208WFP (TN panel). I can say right now that the TN panel is junk when it comes to color and view angle, when compared to the other two. TN is so bad that I don't even used it anymore (gave it to my sister). Between the 20" IPS and 24" PVA, the IPS has better and more natural looking color, and the IPS panel also can tolerate a bigger shift in view angle before the color will act like a chameleon changing its shade. However, I use the 24" more because I need the size, but I love the IPS panel more for its color.
If I'm upgrading monitor, I think only a 24" IPS based panel will suffice, because once you get used to seeing good color reproduction, moving to something lower will definitely be an eyesore 24/7, which is miserable.