With Visual Studio 2008 onwards, we can have some javascripts intellisense when writing our codes. However, Visual Studio doesn’t know anything about MS CRM. So we don’t get a lot of advantage from this but we can extend the use of the intellisense functionality by using
MS CRM Javascript Intellisense Generator
Once downloaded the tool, all you need to do is enter the name of the discovery server and (optional) the credentials, select the organization and save the output. This will create the folder with 1 javascript file for each entity.
If you have Visual Studio open you will need to close and reopen your project to see the new folder.All that is left is adding a reference in you account.js file to let visual studio know where to look for intellisense.
*Updated for CRM 2011 Xrm.Page.
Download this js file
XrmPage-vsdoc.js and now you can have IntelliSense for Xrm.Page.