Virto Cross Site Lookup Feature
Virto Cross-Site Lookup feature allows SharePoint users to reference existing data in SharePoint list easily and intelligently, access list items on other sites, and add automatic duplicate removal and find-as-you-type functionality to your lookups.
The column takes its values from a list on any site you enter in Source Site Url: the same site collection, another site collection or another web application. A filter by a list view and a dependency on another column reduce the values offered.