Perhaps you’ve used the “Favorite Websites” feature of SciLinks, in which you can create lists of websites to share with students.
The new Quiz Manager takes this a step further. You can create questions for a particular website in the SciLinks database and assign students to complete them. You would need to have a class roster first, and then you’re ready to start. There are mini-tutorials on SciLinks that guide you through the process of creating question banks and show what the student activity looks like. You can create “selected response” items (multiple-choice, T/F, matching) and short-answer response questions. After the student is finished with the assignment, the teacher gets a report on how students answered the items and can comment and grade the short-answer ones.

Teachers can work together to create and share a common item bank for a website, or you can choose to keep the questions just for your class.
I’m thinking of how I would use this feature. I was never a big fan of the “read the chapter and answer the questions at the end” type of assignment, unless the students knew there was a specific purpose (e.g., review or preview). While taking a SciLinks “quiz,” the student can have the web page open, so questions for which you expect the students to have memorized the answer would not be appropriate. But I could see this used as an application assessment:

• Apply a unit concept or vocabulary to information on the web. What type of rock is pictured here? a. igneous  b. sedimentary c. metamorphic
• Interpret a graph. The independent variable in this experiment is ___.  a. the elapsed time b. the height of the plant   c. the amount of water provided.
• Gather student reflections, feedback, or questions about the information on a site. What characteristics did this scientist exhibit in her study? or What do you think was the most difficult part of this simulation

Feel free to add a comment with other suggestions for using this tool!
Extra value alert: The tutorials were created with Jing—a free online application that captures screens, cursor movements, and voice and creates a file that can be added to a website or blog. I’ve used this for tutorials and demonstrations. The basic version is free (and fun to play with).