The name is long, and the graphics are certainly nothing spectacular. But the UW–Madison Writing Center Writer’s Handbook website has been a boon to me over the years, as I’ve often had to switch between several different writing styles depending on the task at hand (APA, MLA, etc.).
Although not exhaustive, this site has more than enough information to show you how to format endnotes and footnotes or inline references. They also have a quick reference section for appropriate quoting and avoiding plagiarism. Recently, they’ve also added a podcast for the MLA section and a few downloadable reference guides.
Updates on the site seem to be slow, and there’s little to show what has been updated from the main page. Also, this may not go into enough depth for some purposes. But if you’re looking for quick info, this site will help you get up to speed quickly.