From WPMU Dev: There sure is a lot you need to remember when working with WordPress theme files. From the names of basic template files to functions and how the WordPress Loop works, it’s next to impossible to remember every PHP tag or even how to define a new theme.
Here is a handy cheat sheet, which includes all the files and functions you need to know (but not necessarily remember!) when working with themes. This is definitely one to bookmark and save for future reference!