This is a cool site to checkout and bookmark the tools that you may be able to use at some point. Timelines are great in that they provide a way for students to organize their thinking about a particular topic. Check out some of the timeline tools outlined in this link.
Encyclopedia of the Earth an electronic reference about the Earth, its natural environmetns, and their interaction with society. It is a free, fully searchable collection of articles written by scholars, professionals, educators, and experts who collaborate and review each other's work. The articles are written in non-technical language and are useful to students, educators, scholars, and professionals, as well as to the general public.