I have a small colony of assassin snails that I bought some years ago. Since they eliminated all my ramshorns, they have fed on regular fish food quite well. They are slow to reproduce and are pretty to look at. I recommend them to anyone who wants just a few interesting snails.
Just be very careful with assassin snails, that you never let even one get into the local ecosystem (by flushing one accidentally, etc). In some temperate areas of NA assasin snails have decimated the local snails to extinction. There was talk of making them illegal, not sure if this went through or not in various US states.