So I was trying to think of a good object lesson but couldn't come up with anything. I got on the discussion forum at Pastor2youth.com and someone gave me a great idea. He had seen it in a sermon illustration. It was really cool. Here's the video.
It not only illustrates the idea of one sin leading to another, but also the idea that our sin affects people around us.
The person that told me about it said he saw it with about 100 mouse traps. This is only 48. 100 would definitely be cool!