Depends on the monitor. I'm using a Dell U2412M and according to tftcentral it is factory calibrated pretty well. I've used a Spyder4Elite just out of curiosity and tbh the differences were barely noticeable.
Here's a link to their calibrations and another linkhttp://www.tftcentral.co.uk/articles/calibrating.htm to a guide on how to apply them if you're interested.
