My school used signupgenius, basecamp, volunteerspot and we never got traction and ended up having to use a bunch of tools to make things work. We started using this fantastic tool, SchoolCollabo 2 years ago. It's free and does more than just manage volunteers, it sends out reminders, has these great newsletter templates and lots of messaging, an online school directory, allows us to collect payments, build our own forms, iphone and android app just a ton of stuff.
I highly recommend it, first our elementary school started using it now there are 5 schools in our county using it including the huge high school. I think the url is
www.schoolcollabo.com. Check it out!I don't understand how more people haven't heard about it, but I don't think we could go back to how things were before.