I've been using a dual-monitor setup for quite a while, using a Philips and a Sony LCD. I've never been able to match the colours of the two monitors, and believe me I've tried! The situation got worse when I upgraded to Vista. For some reason ATI's Vista graphics driver made everything look washed out. Out of desperation I decided to get a screen calibrator. I found lots of reviews online for Pantone's Huey and ColorVision's Spyder range. The basic packages don't support dual-monitors so I either needed the Huey Pro or the Spyder 2 Suite. After reading reviews I settled on the Huey Pro, partly because of one glowing review in particular, and also because the device itself is a lot more compact than the Spyder. I have to say, it really worked miracles. Flicking between the corrected and uncorrected modes really shows how unnatural the default colours are. And more importantly, my two LCDs now look ALMOST identical. A lot of people didn't like the automatic room lighting compensation, but I find it quite useful. I'm an avid gamer and none of my games had any problems with it. It can be switched off anyway.
UPDATE: I recently made a move to reclaim my desk-space by selling the 2 19" LCDs and buying a 22" Samsung instead. The default settings on the Samsung gave a horrible blue tint to everything. Whilst it is of course possible to adjust this manually it will never be as accurate as when corrected by proper callibrator. The Huey Pro did an amazing job.