One activity we did was to discuss his famous quotes and then the kids personalized them by telling what it means to them (and a little illustration). The quotes came from All Clip Art as free clip art. I just stuck them onto a powerpoint slide, and copied to fit at least 3 per sheet. Then when it was time to write about them, I had the kids choose what quote they related to the most, they glued it onto their paper, and the rest is history.
Every year to celebrate his birthday I have my students brainstorm their own dream and wish for the world. Since my 4th graders need to practice their cutting skills (I'm being serious), I had them make a cloud/dream bubble and brainstorm on top.
In class we also watched the Brain Pop movie about Martin Luther King Jr, and in the computer lab the kids had a chance to look up every more information about him. Then in groups I had them fill in the posters by Elementary Lesson Plans.
How did you incorporate Martin Luther King Jr. into your lesson plans? Hope this gave you some ideas for next year!