Good ideas include projects that can be made with materials available in the developing world (generic materials wherever possible), are suitable for ages 6-15, and are useful as well as good fun or demonstrate a broadly useful technique. A large number of Instructables already fit these criteria.
OLPC has a wiki
with a discussion of the content they would like to see.
They plan to judge the content by the breadth of its educational value across age ranges and cultural context, by the freeness of its license, by its size (smaller is better), and by the ease of translation (related to cultural context, language difficulty, and the elegance of any images).