I found this one to be the most user friendly and the easiest to use.
This site was originally designed by a student on the UK. HERE is a quick article overview of the program.
Notely is free, easy to use, has a mobile site and has lots of great features.
Notely includes a Calendar, To-Do list, Homework organizer, Notes section, and allows you to organize links, contacts, files, and your classes. You can upload files to keep them organized with your class notes. Tasks in your to-do list have due dates and are listed in that order. The notes function is a fully functional word processor that allows you to add formatting, links, highlighting, and images to your notes. The calendar can even remind you of upcoming events.
Trackclass is a great, free resource for students. The site allows students to track their classes and assignments, and even will send reminders (email or SMS) for upcoming assignment due dates and test dates.
There is also a note taking utility so students can take notes on it if they have a computer in school, or transcribe notes later.
You can even attach files to each class and assignment to keep things organized. It is a great way for students to stay organized.
There is also a version for mobile phones and the iPhone, so students can stay organized no matter where they are.