The journey of Lewis and Clark and the Corps of Discovery is one of the most fascinating stories in United States history. It is therefore one of the most frequently taught topics in US History. From early elementary school through college the story of Lewis and Clark is studied by America students. The most comprehensive source of lesson plans about Lewis and Clark is found on the PBS website. If those lesson plans don't suit your needs take a look at some of these other resources that can be used to teach the story of Lewis and Clark.
Elementary School Resources
Scholastic's Lewis and Clark page features a self-guided virtual tour. A great feature of the Scholastic page is the Scholastic Word Wizard that students can use to find the definition of any word on the page.
The Smithsonian's Lewis and Clark page offers lesson plans for elementary grades and middle school grades. The elementary school lesson plan is titled Animal Encounters. Animal Encounters is a two part lesson in which students draw pictures and write descriptions of the animals Lewis and Clark encountered on their journey.
The Science of Lewis and Clark is a lesson plan developed by a teacher at the South Central Service Cooperative in Camden, Arkansas. This lesson plan is focused on the science of the Lewis and Clark expedition.
The Lewis and Clark Exhibit.org provides a series of elementary school lesson plans covering a number of themes related to the Lewis and Clark expedition. The themes addressed include politics and diplomacy, trip planning, animals, trade, plants, and language.
National Geographic Expeditions offers a lesson plan focused on the theme of mapping. The lesson plan also addresses the justification for exploration and land use.
Middle School/ High School Resources
A member of the Google Earth development team created a Google Earth KMZ file depicting the journey of Lewis and Clark. This file could be used by students to plot information along the trail of Lewis and Clark. You may also consider creating a timeline to use in conjunction with Google Earth. You can find a brief tutorial about adding a timeline on the Google Earth Design blog.
The Smithsonian offers a lesson plan designed for middle school use called "Mapping the Unmapped." This is a five part lesson plan that address geography standards as well as writing standards.
The Lewis and Clark Bicentennial Online Exhibition offers lesson plans for middle school and high school. Some of the high school lesson plans introduce students to using primary documents for research and learning.
The National Archives offers a great lesson plan for high school students. The lesson requires students to evaluate primary documents and images.
High School/ College
On iTunes University I found a fourteen part audio and video series about the Louisiana Purchase. Although it is not specifically about Lewis and Clark, the two videos I've watched were beneficial for understanding implications of the Louisiana Purchase as it relates to Lewis and Clark. The course is produced by the University of New Orleans.