This service lets you put all of your cards in one place. With the premium service (which costs a whopping $20 for the year) you can see at a glance what is due where and when. You can also get email alerts when you get to busy to check the website.
In a quest to stay organized, I found a way to keep track of the many library cards that we acquire. I have one for my local library as do two of my girls and my wife. I also have one for the library close to my work, since they often have something my local does not. So to keep all those books in order and avoid late fees, I turn to Library Elf
Even if you only have one card, the alerts are worth sining up for the service.