If you've got Potter fans in the house, here are some nifty links. We also just discovered the Yahoo 'Hogwarts Summer Correspondance School' too - a terrific (and free) site. You need to register an email address, but then can download lots of very imaginative and whimsical files. Our kids favorites - Hermione's logic puzzles and the mock daily newspapers (you have to join the different subgroups or classrooms - the newspapers are under Literature). Some of the materials these parents dreamed were a lot like my son's Hobbit course through Northwestern's gifted online school (CTD).
Yahoo groups are clunky to negotiate, but there's a lot of stuff there - mini textbooks on 'Herbology' (really Botany and nature activities), Astronomy, etc. Some of the Potter spins are quite clever. Our kids may try their hand at writing a 'newspaper'. For those who study Latin, that is also fun aspect of the books. In fact, HP is now published in Latin as well as Ancient Greek. When J.K. Rowling graduated with double 'firsts' in Classics and French at the University. In fact, she's said she modeled Hermione after herself.
Hogwarts 'Summer School' at Yahoo
Harry Potter Games
The Harry Potter Lexicon
HP Latin Quiz