2 Screens

I've been given the use of an extra monitor at work - so now I have one 19" and one 17" monitor on my desk. I've been given a bigger desk too, but that's by the by.
I have to admit that, mostly, I still use the 19" for the majority of my work, and, as I'm doing web work at the moment, use the 17" as a preview screen.
Windows XP works flawlessly with more than one monitor, and there are a few utilities you can use to add a few niceties. Of these, I've been trying UltraMon out, and it rocks. As well as giving each monitor it's own task bar, it allows you to do things like have one background across both monitors (making a massive panorama), have separate screen savers, and a host of things I've not even tried. I wouldn't say it's essential, but it's definitely worth the tiny cost.
I really like having two monitors - it allows things like having two versions of code next to each other, VS2003 + VS2005 visible simultaneously, and generally a lot less swearing when trying to find the right window - with more of them visible, I can find the one I want more easily.
Despite this, I think that if I were to buy a second monitor at home I'd try and make sure it was exactly the same model as the one I've currently got (or buy two new ones of a different model). At the moment, the 17" at work is just showing colours differently to the 19" and, although with the different pixel size (they're both 1280x1024), it's not easy to switch back and forth quickly.
That aside, I'd definitely recommend - I really didn't think it would make as much difference as it does.