In files like this I don't get the intellisense and this is where I need it most. Does anyone know how I can get intellisense on jquery to work there too?
/// <reference path="path-to-jquery" />
at the very beginning of your js file.
You can also include a reference to your aspx page at the beginning of your js file and intellisense will behave like you are on the page.
/// <reference path="mypage.aspx" />
You might want to take a look at the reference for the reference tag.