My dyad instructor recommended ReadWriteThink.org to me. It's fairly easy to search for lesson plans based on grade level or age, as well as topic. I used it to find creative ideas for a writing lesson I taught near Halloween. The site is huge! :)
This is a another great resource. It has tons of different lesson plans, ideas, activities, etc. Best of all it is free! You can register as a teacher if you want to to organize what you find, but it is not nescessary.