Male circumcision

The wikipedia article link has a ton of good info from both the for and against sides. Religion, culture, and family history seem the biggest reasons out there now.

Some people do it to make their child feel "normal", although with the amount of men who are uncircumcized nowadays, that's not much of a good reason. Some studies have shown that there is a lower risk of STD's for men who are circumcized because the foreskin provides a warm, moist environment which allows bacteria to thrive more easily. But the risk isn't that much different. Really it comes down to personal choice.

Some babies may be born with acute phimosis or develop it later in life. This condition causes a constriction of the foreskin over the glans, which prevents them from freely moving the foreskin back. Some would consider circumcision for that. I know I will if I ever have a boy because I have phimosis and I wouldn't want my child to have to deal with that. It could also be a family tradition in men to some.