Lets talk about SNAILS!!
There are many different types of snails in the hobby, and lots of them get a bad rep. I personally LOVE snails, and think every tank should have some (pending the tank-mates). There are snails that multiply like crazy, and some that don't, but they're all a great addition to your clean-up crew, and can be a very good indicator of overfeeding. 
Snails, like ramshorns and trumpet snails, will multiply very quickly in an overfed aquarium. I use these as an indicator that I am overfeeding. Its great that they are there to consume any uneaten food, but you don't want them overtaking your tank. Once you cut back on your feeding amount, the colony of snails should subside.
If a colony of snails is not your thing, then look toward the Mystery Snail. These guys are amazing maids, and the great thing about them, is that they do not lay their eggs under water. They are not hermaphroditic like ramshorns, meaning they need a male and a female to reproduce. Since they lay their eggs above water, its very easy to spot a clutch of eggs and take care of it before they hatch (roughly 3 weeks) if you don't want a bunch of Mystery Snails.
Nerite snails are another popular option. These come in a variety of patterns (such as tiger nerites, red racers, red spotted, etc) and some even have horns! These are great algae cleaners, and the best part is that these will NEVER reproduce in your tank. They may lay eggs but the eggs will not hatch unless they're placed in brackish water.
Rabbit snails are another that won't overcrowd your aquarium. These cone-shaped snails range from generally 1" up to 4.5" in some species. They will mainly stay buried in the substrate during the day (which is great to keep your substrate stirred up), and come out to eat after lights out. These reproduce very slowly, growing the young inside the female's brood pouch. Once they have grown enough, they will be laid in an egg like shell casing that will dissolve and hatch a fully developed rabbit snails. They only release one at a time, so they are an extremely manageable snail.
If you have a colony of snails that you would like to eradicate, but you just can't quite get the upper hand on, you may look to the Assassin Snail. These little guys are small, cone shaped snails with a beautiful stripe pattern. They may look sweet and innocent, but they will massacre pest snails. This method of eradicating pest snails is not personally my favorite, but lots of people suggest it as an easy fix. Either way, just remember that these are carnivorous snails and may need supplemental feeding once they clean up a colony of pests.
