A WebQuest is an inquiry-oriented activity in which most or all of the information used by students is online.
By providing links necessary to complete the quest, the student is able to focus on the material rather than spend time looking for it. The five-part WebQuest (Introduction, Task, Resources, Process, Evaluation, and Conclusion) promotes critical thinking at the levels of analysis, synthesis and evaluation. http://www.netnet.org/students/student glossary.htm

The WebQuest Page
Weaving the Web into Your K-12 Curriculum-A WebQuest designed for use with pre-service and in-service teachers
WebQuests at LITE resources for Teachers The What,why, and how of WebQuests, + links
Webquest links from Oswego City School District

Specific Examples:
Iroquois WebQuest
Blogging: It's Elementary!