Xyle Scope is a really neat app from Cultured Code.
If you like CSS and to know how people like to wire up there code this is a really useful application. It is basically an internet browser interface where you can navigate to the site you want by URL as you would. Then in the section of the interface to the right you can see the layout and the cascade of the stylesheet. When you select a snippet of code. For example a div tag in which site content is contained. It would show you the CSS rules which have been given to that snippet of code, such as a width, height, padding margin and so on.
Here is a look at the interface displaying my friend Sam’s website.
I seriously recommend this, though I am only using a trial at the moment.