Stephanie Thornton and L.T. Host have both already heard about the wonder that is TVTropes.org, but I wanted to share it with the rest of my blog-friends.
The site's original purpose was to gather examples of the common storylines, characters, settings, etc that exist in television shows. It expanded from there to include movies, literature, anime, and real life in certain cases. These "tropes," as they are commonly called, are things you can reasonably expect readers of a certain genre to know about already.
For example (from the entry for Analogy Backfire):
"Roger makes an analogy comparing someone to a well known source, often intending to sound positive. Rita then points out a further fact about the analogy, often inverting the meaning, and often painfully near the knuckle. A common example is someone comparing two lovers to Romeo And Juliet, which suggests they've not read the ending (or the beginning, or the middle) of the play."
Each entry has an opening quote that is sometimes called the "Trope Namer," also known as the foremost example in that particular category.
Why would these things be useful to writers? Well, by seeing these vast amounts of examples for various characters, dialogue, etc., you can determine how detailed you need to get with description, stock characters, setting, and a whole bunch of things.
Pretty much the only downside is that following the links can kill an entire day that you would've otherwise spent writing. I'm sorry for that, but I still maintain that the site's usefulness cannot be understated in providing source material and other goodies.