When I took Gen Bio last year, we studied the lac operon. In Genetics this year, we studied it again (in more detail and depth, of course). My professor found this awesome online lac operon simulation that lets you “mutate” (i.e., remove) certain elements of the operon, add lactose to the system, etc. Best of all, it’s free. I highly recommend it for anyone studying this. It’s also just kinda fun … in a super nerdy way. 
Here’s the link …
lac operon simulation