http://www.youtube.com/watch?v=hjFMi5i-2GI
Here is a video of my apple snail cleverly named banana. I really love this snail and it serves a dual purpose as a great glass cleaner! The snail currently resides with some bala sharks and tinfoil barbs. I have even had it in a tank with a few rainbow sharks who never bothered it, even though they were fiercly territorial in the tank.
The snail does have the drawback of being able to have TONS of babies at a time. The LFS where I bought this snail also sold me another one, lying to me when they said it wouldnt be a problem. I did have a smaller tank get over run by the snails and four clown loaches couldnt take care of it. I finally had to take the tank down for two weeks or so and even still, I had a couple survivors.
I suggest that if you were going to purchase a snail, ask for one that has been by itself for a while or quarenteen it until you know it isnt pregnant or about to lay eggs. This way you can be sure you wont get over run. Dont let this discourage you though! Snails are great for a lot of reasons and trust me, unless you have fish that love to eat snails like loaches or puffers, they can close up in that shell faster than you may think. Mine has survived a lot of picking on by other fish who were curious about it. Now I even move the snail from one 55 gallon tank to another so that it will clean up the glass when my pleco or algea eater gets a little bit behind. They are also great at keeping decorations clean since they can get into all the nooks and crannies!