If you have Packet Tracer from the Academy, then it should have come with exercises. If you downloaded it from some site, then ...
I'm thinking that Global Knowledge and other training providers have virtual courses that include access to "labs".
GNS3 is also a possibility if you need to practice in a virtual environment.
Personaly, I used Wendell Odom's books and GNS3 to do most of my practice. I had access to a couple of switches for practice.