imo i would go for dual, or if you have the money triple. i don't think you can get enough pixels on even a 22 inch screen that you can with 2 x 19" screens, no matter how good your graphic card / monitor.
Dual (or more) monitors are the best thing I ever I ever added to my desk. They are a real time-saver and make it quite easy to multitask in ways that you can't with just a single monitor...no matter how wide it is.
Ditto. At work I run a 20 inch Mitsubishi DiamondPro and a 17 inch Compaq. At home I use my Vaio notebook with a 16 inch display plus a 19 inch Samsung LCD display.
Dual monitors really expand your work space. The main problem I see is trying to get gamut synched between them. I've yet to get the monitors to display exactly the same, with my work desktop or the notebook at home.
I have a 17" proview and a 17" viewsonic. They display exactly the same, even though the res on the proview is 800x600 and the res on the viewsonic is 1600x1200. I tweaked the gamma on the proview so the color matches the viewsonic (I like it better, others might like it better the other way - a case of "redder whites" opposed to "greener whites" with me preferring the "redder" version....) I had to do a bit of alignment tweaking as well.
Matching may depend more on your vid card than your choice of displays: it was virtually impossible to "match" these with my previous nvidia card (whose model I don't now remember); it was pretty simple with this one: GEForce FX 5500.
I don't think I would go back to one monitor, even if offered a "tv" sized one....