Nerite snails cannot breed in freshwater, they require at least brackish in order for the eggs to develope. Kinda hard to find though, http://azgardens.com/aquarium_snails.php or this lady has them, though her page doesn't seem to be working right now.
apple snail. Not a sexual If it turns out to be pregnant they ly eggs above the water line so just knock them in. The fish will eat it or the eggs would drown.
Pomecea bridgesii. get about golfball size,need 2 to breed,and lay eggs above the waterline,easy to get rid of if you dont want young.I like the purple ones
here is a pic of my cana apple snail. and another pic of what they are able to do. if you want more than one and they breed. do as Jeox said and either push the eggs into the water or use a razor blade to remove the eggs and throw them away. I let mine breed and the second pic of what happened in a little more than 2 months.