An excellent source of notes is Matt's Web Page, which contains IB Chemistry, Biology, Math and Physics notes. Last time I checked, the math notes were not yet fully up, and the biology seemed to be lacking in some sections. Make sure to check on it though.
Make sure to visit the IB Webring as well. Its a collection of IB related sites (37 so far) written by students and teachers around the world, who have all experienced the IB.
Extended Essays looming up? TOK papers? Need inspiration? Check out IB Papers, a collection of TOK essays, extended essays , World Lit. papers and other writings written by students and submitted to the IB.
For a satirical look at the IB, visit IB Stressed and laugh while you cry at the tortures of the IB.
IB.Net:
The one and only resource site for your IB needs. Includes an exam database, a discussion forum and even a IB-bookstore. We are currently looking for columnists, please apply.