SharePoint's built-in tools are good at providing a basic interface for adding and editing data, however, there are times when the included editing features aren't enough. There are applications where the SharePoint list will work, except for one small detail. For instance, you may need to ensure that one of the fields in your list matches a back-end data source. This might be accomplished by creating a drop-down that is populated from a back-end system, or perhaps it's some custom validation that ensures that the data that the user enters is in the back-end system.

http://www.devx.com/webdev/Article/30026/