If you stare at a monitor for 8-12 hours a day looking at code, I have a couple questions for those that may have researched the health factors of this or have tried a few options.
I have a 24" Dell at home, but I doubt many companies would consider that for a development machine.
22" Wide with a resolution of 1680 x 1050 is good, and the price of those monitors are relatively cheap now.
Currently I am working on a 17" 1280 x 1024, as the laptop I got to dev on only got a meager 1280 x 800 screen, which is pretty much useless for coding.
IMO 2 x 17" or 19", or 1 x 22" or larger.
Note: most cheap LCD's have terrible color, example the orange on SO, looks a pale yellow, and thats the best I can get it. The Dell at 5 times the price of a cheap 24" does not have these issues, but you pay for it :( (I still think it was a damn good investment)!
24 inch is minimum for me, and 1680x1050 is too few dots for effective coding. I prefer dual monitors at 1920 x 1200 or better .. i'd really like a pair of 30 inch Samsungs but I need to get richer. Brightness and all that other stuff has never much affected me .. since i'm always coding at night anyway not much of an issue
I've always used the analogy between monitor size (resolution) and desktop size - larger screen, more space to spread out and work.
More important than the physical size is how you set it up - most people have their monitors set way way too bright.
I typically start with maximum contrast and minimum brightness, and work from there. The black on your screen should be real black, not dark gray; the white on your screen should be no brighter than a piece of paper held up next to it.
That said, I do have good screens. At work, dual 22" 1680x1050 LCD; at home, dual 19" 1200x1024 CRT; and my laptop is 1920x1200 17". I've trialled a single 24" LCD - was really nice, not as wide as either dual monitor setup.
Updated 1 Mar: The suggestion from rtpearson to look away from the monitor regularly is good advice.
I was told (years ago) that it is important for your eyes to change focal length regularly.
If you have a seat next to a window, glancing outside while you think is a good way to achieve this. "Walking an email" to a colleague on the same floor can help as well. Using a timer (such as this one I wrote) to remind you to take breaks and rest your eyes is also useful.
I'm not sure it matters. I've worked in investment banks where multiple high-res screens were the norm and am currently doing development work at home on a 9-year old Sony laptop with a 1024 x 768 screen. I haven't noticed any difference in my productivity or my eyestrain in those very different envirobments.
In terms of brightness, what works for me is to adjust the brightness of the display to match the ambient light in the room. At the moment I am running a 24" Samsung Syncmaster and I have to say that I consider leaving it on the brightest setting to be a health hazard.
If you're worried about eye-strain, don't forget the low-tech solution: every 30 minutes, lean back, close your eyes, and rest them for 10 seconds. Or, if you don't want to look like you're napping, gaze out a window or across the room. You should do this regardless of whether you're staring at a monitor, a book, or a sheet of music. Staring at anything for hours at a time is going to strain your eyes.
I use a free timer program to tell me when 30 minutes is up. Whenever I forget to do this, my eyes always feel itchy and tired by the end of the day.
I know this doesn't answer the precise question you asked, but I think you're looking in the wrong place for a solution. Rather than investing in a new monitor, just rest your eyes on a regular basis. There. I just saved you a few hundred bucks.
EDIT: References have been requested, so here they are. There's a decent scientific article on the value of microbreaks here and a review of the literature here.
There are lots of websites to help you calibrate your monitor brightness/contrast. This is just one http://www.displaycalibration.com/brightness_contrast.html
If you use a CRT screen, make sure you set the refresh rate nice and high. 85Hz is a good value. The default rate on Windows of 60Hz is too low. The flickering makes me feel nauseous. The refresh rate on LCD screens doesn't matter due to high "persistence".
Most people don't know this and leave their screens at 60Hz. Strangely, however, from personal experience, if you tell them directly, "Your refresh rate is wrong", many of them will get defensive—about their refresh rate!—which they probably don't even know what it is. People are strange. I'm glad LCDs are replacing CRTs.