"The Magic School Bus: Inside the Human Body" by Joanna Cole (DVD also available; sometimes shown on Discovery Kids channel)
"Skeletons" (Scholastic Science Reader, Level 2) by Lily Wood
"Bare Bones: All About the Human Skeleton" by Elise Richards (includes a 12" tall glow-in-the-dark skeleton model to assemble)
"Understanding Your Muscles & Bones" (Usborne Science for Beginners)
"The Search for the Missing Bones" (a Magic School Bus chapter book)
Human Body for Children: eight videos for Grades K-4 from Schlessinger Media; available at almost any library
The Magic School Bus videos: three about the human body, For Lunch; Inside Ralphie; and Flexes Its Muscles. Lessons plans for the DVDs are free at Scholastic.
Interactive Body Site from the BBC: amazing site with games and fabulous human body info
BrainPOP: a few free human body interactive games
Human Body Unit Study: It's prepped already! Worksheets, lesson plans and more.
The Virtual Body: online tour of the body; for older folks
Human Body eBook: online book of the body; for little folks
The Human Body Jigsaw book by Dr. Malcom Clark (five 48-piece jigsaw puzzles; skeletal system, central nervous system, circulatory system, muscular system, digestive system)