The synopsis. (Imagine scary music . . . and cut.)
I'm not the only one who hates writing synopsis, or who feels that cold sinking of the stomach when I look up an agent's guidelines only to find he/she requires one. A query is a teaser, but the synopsis is your entire book in four pages. (And I'm a believer that epic fantasy is especially difficult to weed down to four pages. I would really, really love to see a synopsis for The Game of Thrones.)
But, a match in the darkness, I did find a helpful blog post via Suzie Townsend a little while ago regarding the synopsis; she offers three solid tips for writing one. If you're in that boat, or plan on being in that boat, I recommend checking it out.
Meanwhile I'm helping my sister move and setting up the Christmas tree. ;)