Finding and keeping track of volunteers is an integral part of organizing any event. VolSched makes this task a bit easier. Create an event, add jobs that need doing, add shifts for which volunteers can sign up, and give the handy URL to potential volunteers. They can decide what they want to help with and when they want to help, and you can see who has signed up. You even get the option of making your event findable to people without the URL, so you can recruit volunteers using VolSched itself. Your volunteers only need to enter their contact information once to volunteer for all the events you (and others using VolSched) hold.
Best of all, VolSched is entirely free to use.
The source code is now available on GitHub. Please feel free to submit patches or pull requests if you make changes!