I use the Pantone Huey Pro @ work, and that combined with a correctly calibrated printed/plotter/proofer you can get some very accurate results, especially for print output. The Huey works very well and is very easy to use, also works with multiple monitors and have a set of variable options such as screen temperature/target white adjustment.
The difference a decent calibration tool can make to a monitor is unreal, especially when you look at the uncalibrated settings you ahd before. Blacks are deep, whites are clean & the range and accuracy of the colours especially when soft proofing in photoshop/preview (mac OSX) are very very close to the final output, especially if you recalibrate once a month.
It just takes the risk/guessing out of the equation, and to date my Huey has to its name a tricky 1 Million unit packaging run, a weekend full page ad in The Times & many other packaging based projects, all of which handled completely different ouputs/profiles but every time the results have been spot on!
Well worth the pennies spent tbh!
Remember screen calibration will only give you faithful colours on screen, to get accurate print output your printer needs calibrating too.
It needs calibrating to the specific paper intended etc.
This is true for ultra accuracy, however most of the big boys such as Epson & Canon provide a range of reasonable output profiles for their range of printers that are ideal for small company/home use.
Simplified you have to calibrate your screen, then print; matching the correct paper type (coated, uncoated etc) in the printer options with the correct printer profile. Do this properly and you will see very reasonable results.
Hope that helps mate!