I've pegged these two as Arion hortensis. As you can see, one is a dark slate gray with an orange belly while the other is a lighter gray with a pale belly. I'm fairly certain that they're different color morphs of the same species. At last count, I have three, but I suspect that there are a few more hiding in the main tub (they're all kept in clear storage bins).
This ornate little guy is an Anguispira alternata, or flamed tigersnail. This photo was taken by my mother, who is a talented photographer. It was like glamor shots, but for gastropods.
Another photo by my mother. I believe this snail to be Oxyloma elegans, a species of ambersnail. I was fortunate enough to find two, so I have a (hopefully) breeding pair!
This snail is about half a centimeter long. It's really hard to accurately identify something so small, especially since there are many other species of this general size and appearance. However, I'm thinking that he may be
02/08/13 EDIT: This snail is actually a Cochlicopa lubrica
I have no idea what kind of snail this guy is. He's a very plain brown, and the underside of his shell features an umbilicus, like he has a belly button.
02/08/13 EDIT: This snail is a Triodopsis tridentata
Last, but certainly not least, is the largest Deroceras reticulatum I've ever seen. He measures more than 2 inches in length. I was fortunate enough to witness him mating with another, comically smaller, D. reticulatum, so hopefully I'll get some giant babies from him.