I use a Spyder 2 Pro - it came highly recommended by several commercial photographers I worked with. Does the job perfectly and I have no complaints. The only other one I've used was a Monaco Optix - again it worked as it should, but I only used it once for a print job so have no long term experience with it.
Some people do seem to have problems with some models - don't know if it's a monitor or a computer issue or something else but generally they all do their job well. There's lots written about calibration, it's a bit of a black art. Have a read of
http://www.drycreekphoto.com
Edit - I use an Apple Cinema display as did the peeps who recommended the Spyder. So, there may be a link... they seem to work well together.