Absolutely. And even if you don't care that your cat is out there making kittens, it's important to know that un-neutered males are much more likely to get into fights with other cats. A lot of the nastiest feline diseases spread through fighting, and fights result in injuries that can easily become infected. It's not unheard of for males to lose eyes (or even whole limbs) to completely avoidable infections.

So neuter your damn cats. It has the potential to extend their lives significantly, and promotes a healthier cat population in general.