Stephen Malinowski at Cool Tools discusses the benefits of single large displays compared to two smaller displays. Purchasing two smaller displays has long been the economical choice—two 21" LCDs were much cheaper than, say, one 30" LCD. Malinowski notes that the price differential between the two is decreasing; he also notes the benefits of having a single larger display:
I found that once I got used to the idea that most things could be expanded to a size that required no window scrolling, I began to "think big" about a lot of things: my spreadsheets got bigger, my diagrams got bigger - and more unexpectedly: the size of the kind of thing I thought I could handle got bigger; and because I was much less often having to chop things into smaller pieces so that they could fit, things got simpler.
It's a no-brainer that more pixels is usually better than less for knowledge work, but the vertical (usually) gap between dual monitors makes it difficult to use them as a single space. Instead, multiple monitors are separate but tightly coupled spaces.
Here are the rough prices (via CDW.com and Dell.com) for some options:
Apple Cinema HD 20" LCD: $599
Dell EP207WFP 20": $229
Apple Cinema 30" HD: $1,799
Dell UltraSharp 3007WFP-HC 30": $1,199
I'm not sure of the overall quality of the Dell displays above, since those are Dell's lowest-end versions of the displays in each size; the 30" 3008WFP is $1,9999. And as Malinowski notes, there's a fairly large pool of used monitors available at places like eBay to further reduce prices.
[via Cool Tools]