Here are some of Rhonda Wilson's shots:
http://naturalaquariums.com/inverts/snails.html
Any possibilities?

On the bottom of the next page is an example of Physa. Mine are all black and not as attractive, but pop up from time to time and are no problem. The site has a bunch of other snails I'm not at all familiar with, but take a look at the common pond snails on the next page. I remember a lot of these, while (as a junior high student) perched on a log in my favorite swamp - now a housing development. :(  And they had the coolest amphibians swimming around in there.

http://animaldiversity.ummz.umich.edu/site/resources/jack_burch/index_0060.html

Click on the black Physa from the search page below. These are less than 1 cm or 1/2 inch, that is about as big as they ever get. The great William Innes praised them 70 years ago in his Exotic Aquarium Fishes, but did admit they could get a bit numerous.

http://images.google.com/images?hl=en&q=Physa+snails&spell=1

The following site also was stumbled on. There are some really neat shots of Apple snails (which I would not trust with plants.) Yesterday, while tearing down a lot of tanks, I found an apple snail graveyard, way behind everything, where some of them must have crawled after eating everything when I had them on hair algae patrol (years ago).

I guess if one has apple snails, they must cover the aquarium top just about as thoroughly as they would with swordtails or killies.

http://sunrisecreek.net/Desktop/Aquarium%20Snails/