Since Glogster has revoked all free education accounts for a class, I'm recommending a few alternatives.

Glogster is just the latest in a line of websites that took away my education account after they encouraged me to join for free and use their service for free. It seems to me that the teachers who used their service and advertised for them, should receive better compensation than to lose their student accounts.

Altec's 4teachers.org has a suite of free services for teachers, and the one that is most like Glogster is called Web Poster Wizard. I've used it in the past to construct webquests, project based assignments for students.

With Web Poster Wizard, you and students can make posters. You can also create a class and keep track of student work.

Big Huge Labs has many excellent presentation tools that can be used like Glogster, yet they don't have a way for teachers to contain a class.

Otherwise, you can use the old standbys like: GoogleDocs Presentation or PowerPoint to help your students enhance their learning through projects.