lots of lessons related to the brain and the nervous system. Addresses topics such as how neurons fire, addiction, memory, brain dissection, and much more.
Interactive game from sciencenetlinks. Put Arnold's organ systems together before time runs out (covers digestive, cardiovascular/respiratory, nervous systems). Not super detailed, but could still be fun as a quick activity even for upper grades.
An amazing science site with a large number of magnificent animations and graphics to help you explain science principles. Content suitable for older students.
http://ictmagic.wikispaces.com/Science