SharePoint Cascaded Lookup
Cascaded Lookup is also a lookup tool with powerful features that establishes relationship with lists. It creates more choices on dropdown menus but at the same time cuts down choices as data is specified within each drop-down menu, thus also cutting down lookup time.

SharePoint Cross-site Lookup
Cross-site Lookup is a much simpler but feature-packed lookup tool that gets information from any site in a site collection. A find-as-you-type functionality filters items displayed in the lookup field according to a view defined in the source list.

SharePoint Lookup Tracker
Lookup Tracker - summarizes all information related to an item in a list. The page displays not only all items from which this item looks up, but also all items which look up information from this item. A "Related Information" link displays all connected information of the item.