I've got the Gretag Macbeth Eye-One Display 2 (running on XP Pro), and I'm using it with a LaCie Electron Blue IV 22" CRT. In my humble opinion, that's about as accurate as you can get.
Although I only ever work on my pictures when the light is the right temperature or I can close the blinds and switch on my daylight light bulb. There's no point in calibrating your monitor in one light and working in another - might only be a small difference, but could make all the difference.