The Seven Deadly Sins of Punctuation And How You Can Avoid Them (Note: Read carefully. They preface each "faux pas," telling you the correct usage, but provide the WRONG way as examples. It's confusing).
This chart from Grammar Girl Presents the Ultimate Writing Guide for Students gives examples of the 15 most common ways to use a comma. Some of the items represent style choices instead of rules, such as how to use a comma in a list, but when you're making a simple list, you have to make choices