Google Apps offers:

Standard Edition  : Suitable for 10 users and basic applications. Free

Premier Edition    : Suitable for businesses of all sizes wantng more space, email storage, inclusive more business apps as
                          well as powerful email security. £33 per year per user

Education Edition : For educaitonal institutions ( all features of premier version but free, however you need to qualify
                          google terms for education institutions)

Click here to compare Google Apps Edition 

Google Talk – Keep students in contact even when they’re not on campus, with instant messaging, file transfers, and voice calling over the web.

Google Calendar – Google Calendar makes it easy to organize schedules and share calendars with others.

Google Docs – Enable students to collaborate real time on documents, spreadsheets, and presentations, across campus or around the world. Learn More

Google Sites – Google Sites makes it easy to share all types of information, without any technical language to learn and access from anywhere. Learn More

Other Google Products made available in Google Apps

Other Business Applications from Google Apps Marketplace that integrates within Google Apps