(Rating: 5 out of 5)
Without fail, when I and other Officetalk SharePoint Consultants are assisting with SharePoint projects we get the dreaded question: "Yes, but how do I add another level to the list?". Ok, the wording changes, but they all want to have a drop-down list based on the entry they entered on a previous list.
The basic SharePoint Lookup feature is quite basic and just gives a list of the entries on another field on the current site. Yes, with SharePoint Designer and Data Views you can combine data from lists on several sites, but it is quite a complex process. Out of the box SharePoint falls short here, but SharePointBoost's Cascaded Lookup takes it to the next level.
Being a football fan (the great Aston Villa) I have used Cascaded Lookup to set up a European Players list. It starts with all the European Countries and the leagues in each and then has a list for each of the teams in each league. So, now using Cascaded Lookup the user can enter an individual players’ details and have a field called 'Team' that is filtered first by Country and then by League.
It may get slightly confusing when trying to add a secondary filter (i.e. filtering City by Continent and then by Country), but overall Cascaded Lookup is a simple, but a very useful tool. It is also very reasonably priced, and offers a free 30-day trial.