Since I've been traveling I haven't had much of a chance to research resources for The Great Gatsby. At first glance, there is a lot available, but I'm not sure how good many of them are. I'll pass along a few I've had a chance to visit. Please add anything you found and liked in the comments and I'll include them as well.
Wikipedia's entry for The Great Gatsby, which has many more links and resources listed. I'm not providing the link to the text here since it appears the book is still in copyright.
From The Literature Network
A school project website, with background and many links as well
From Homework Online
The University of South Carolina's Fitzgerald Centenary site
Hudson Gevaert's "The Great Gatsby: A Beginner's Guide"
From Barry, some additional resources I missed:
The F. Scott Fitzgerald Society
Since the novel's time sequence takes place during the early 1920's, a review of Prohibition is salutary: Wikipedia entry on Prohibition