Over a year ago, I wrote up a quick and dirty analysis of display prices. Seems like a good time to revisit that now.
First, I’ll note the differences in prices since last time:

• A Dell 30 inch (3007WFP-HC) is now $1189 (down from $1700 for the non-HC version)
• Apple’s 30 inch is now $1800 (down from $2000)
• There are several other 30 inch contenders, including Gateway (~$1700), Samsung 305T (~$1250)
• Low end 20 inch displays are now $250 ~ 300 (down from $400)
• High end 20 inch displays are now $800 ~ 1000 (down from $1200)
• Low end 24 inch LCD displays bottom out around $350
• High end 24 inch LCD’s are around $700, except for the Eizo’s which are still around $1300 (down from $1700)

Also new is the introduction of the 27inch form factor, which still sports a 1900×1200 resolution, which enter around $1000.
Based on this info, I calculated the same price per display square inch, and price per kilo-pixel as I did last time. For the price of each monitor size, I looked around and found that model that I would pay for, and took that as a representative price. I’m probably picker than most, so results may be different for you.

As expected, the 30-inch model is cheaper per-pixel than the 27 inch models. The 27 inch models seem like an especially bad idea if pixel count is what you’re after. The 20 inch is still the cheapest, both in terms of physical display area, and pixel count. The price per pixel of the 24 is closer to that of the 30 than it is of the 20.
Update: Some math corrected.. my spreadsheet had the 24 and 27 inch models as having 1600×1200 resolution instead of 1900×1200. That makes them a bit cheaper in the price per pixels column.