Better calibration tools for different monitors?

I have an older (early 2008) MacBook. I've finally gotten to the point that, each time I readjust my sitting position the whole thing changes! I've 99.9% decided on an HP ZR24w monitor for it and want to get a calibration system at the same time. In various posts on various sites I've occasionally seen mention of how one system works better on one monitor or "Don't get x system for y monitor", etc.

Is there actually one I should consider over another for the reason of monitor choice?

I can't seem to figure out what difference the various ones have from each other, even within brands. (Spyder3Pro and Spyder 3 Elite - just the projector capability??)

Would appreciate info or direction to a post/reference that nicely outlines it for non-techy people.

Thanks so much.