Widgets are a great tool and resource that can pep up a website. There are great ones that can promote new books, share photos, provide Twitter updates, and more. Like with most things in life you do not want to overdo it. This goes back to usability. Does the widget truly serve a purpose? What is its use to the student?
Having too many widgets can slow down the page's load time. Some widgets will clash with others, giving errors. Lots of blinking, scrolling, and movement can distract and/or confuse students. Limit your widgets on a single page. And make sure they work properly on all operating systems and devices.
Consider these widgets: