Conditional Drop Down List w/ Large volume of Data

I am trying to auto populate dependet drop down lists from a table with a decent volume of data but unable to find a way to do it quickly, without having to manually create and reference each item. Has anyone found a solution to this problem?

Nice tutorial here just try :

http://www.excel-easy.com/examples/d...own-lists.html
http://www.contextures.com/xlDataVal02.html
http://chandoo.org/wp/2008/11/25/adv...-spreadcheats/

Thanks Azumi. One of the links worked but now when it pulls in the data, I received duplicates as the results occur multiple times. Do you know how I can tweak my formula below to have duplicates deleted?

=OFFSET(ListStart,MATCH(C12,ItemCode,0)-1,2,COUNTIF(ItemCode,C12),1)

https://www.youtube.com/watch?v=3u8VHTvSNE4

tutorial from mrexcel how to remove duplicates for drop down list