The first one is Lesson Plan Central. This site is a large repository of lesson plans and links to lesson plans for every topic and grade level. It is easy to navigate, has a huge number of resources, and is free. There are some great lesson plans on this site. I have used some as is, and used others with my own modifications.
The second one is Discovery School's Lesson Planner. This site is an online lesson planner that any teacher can use. Lesson planner allows you to create and store your lesson plans in your account on their server. You can edit, print, or download your lesson plans to your ocmputer as needed. You can also link to other items you created on DiscoverySchool.com, such as puzzles, worksheets, and quizzes. This is a great resource for teachers. By keeping all of your lesson plans on a web server, you will have access to them from any internet connected computer. You can also use all of the other resources at DiscoverySchool.com. Discovery School has a ton of resources such as the ones listed above, Kathy Schrock's Internet Guide, Science Fair Central, and a Lesson Plan library of already created lesson plans. Discovery Education has a large number of resources for educators and a majority of them are free.