I guess I shouldn't be surprised but possessing the Apple snails, which in many places in the world have become vectors for disease organisms (such as nematodes which can cause the potentially lethal eosinophilic meningitis) and are a serious threat to crops in several places in the world have been banned in the US as of April 5, 2006. Importation and Interstate commerce of the more benign "Mystery snail" the Pomacea bridgesii can be done but with a federal permit. So that they can be properly identified (by some one familiar with the Pomacidae) they must be over the minimum of 1.4 inches (3.5 cm) long.
http://www.ekkwill.com/usaqsnailban.html

Unless you have a local shop carrying these, brought in under permit, that is the end of them in aquaria for many people. Clubs are rightly reluctant to let any of those snails into auctions. Retailers, including Internet sellers, have often backed off of them. For example see http://www.azgardens.com/pond_snails.php

Partly because of these bans and partly because aquarists have been so frustrated by large crops of little snails, there has been a significant increase in interest in the algae eating nerite snails also called Olive Nerite Snail, Olive Nerites or Olive Snails. Neritina reclivata is usually found in brackish waters (where they breed very well) and marine waters. Evidently though they may lay eggs in freshwater, those eggs aren't supposed to properly develop!

Salt water aquarists are also discovering them. They don't get as big as some algae eating snails and that is another one of their virtues.

Aquarists can and do breed them in brackish water. That was the origin of mine. Eight level tablespoons of sea salt per gallon should do it. They can also be fed squash and probably the veggies we feed our bristlenose "plecos." They might take to dried seaweed such as Nori.

I recently picked up a bag of them, though I miss-spelled them when mentioning that here a couple of weeks ago. They seem to be climbers and I covered them pretty well. In quarantine they ate all of the algae flakes given them. One will hear that they do need a fair amount of calcium in their water (most "unsoftened" Midwestern well water will take care of that). One does not want them to be in a tank that is dirty enough to experience a pH drop below neutral or 7.0. A higher reading is better for them and happily, also for guppies and virtually all hobby live bearers.

Four were just put into a planted tank with a little soft algae. We'll see how they do and if their appetite for algae matches the internet accounts of them.

Sometime, perhaps next spring, I would like to mix up a tank of brackish water and add crushed coral gravel to buffer the pH up and provide extra calcium in the water. Hopefully they will breed with heavy feeding and water changes.

Have kept various Pomacea (and having never released them into the wild except when raccoons broke into container gardens and ate them) I find the olive nerites are quite dull in coloration. There is hope though, nerite snails are found in a number of locations around the world. There are studies on one from the Middle East for instance. I do not know how brackish their water is.

There is also a very attractive Zebra Nerite or Neritina natalensis. The name suggests that it is from South Africa. For a nice photo see
http://www.petfish.net/articles/Invertebrates/Zebra_Nerite.php

Drs Foster and Smith market a couple from the Caribbean (Nerita tessellata?) and Pacific coasts of Mexico. These are also quite attractive and again may need a lot of salt in the water to successfully breed. Interestingly those species are listed among their marine offerings. The olive nerites are carried among their freshwater invertebrates.

http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=1472

There are also the Nerita species. I was startled by the term Virgin neritinas. (Are there also promiscuous neritas?) It turns out that they are found along the US Gulf coast to Brazil and are formally called Neritina virginea (after the state, which of course was named after the "virgin queen" Elizabeth I of England). They may be especially common in mangrove swamps, whose water chemistries vary with the tide.
http://www.backyardnature.net/yucatan/vitta_vi.jpg

There evidently are over 280 species of nerite snails, mostly from tropical and subtropical areas.  There is even a European common river nerite (Theodoxus fluviatilis).

http://www.weichtiere.at/english/gastropoda/freshwater.html

If you Google images of nerite snails (or Nerita or Neritina or Vittina or Neritatidae) you will hit sites like this. Clearly I know very little more about them than probably do most of us, having picked up most of this recently on-line. If someone happens by who has had some experience with nerite snails, please share your experiences. For freshwater tanks we might be best served by nerites from coastal marshes and swamps. Of course, those tend to be among the more inclined to wander out of the tank, so be forewarned. :)

http://www.conchology.be/en/availableshells/searchspeciesgallery.php?family=NERITIDAE